1	// SPDX-License-Identifier: GPL-2.0-only
2	/*
3	* fs/fs-writeback.c
4	*
5	* Copyright (C) 2002, Linus Torvalds.
6	*
7	* Contains all the functions related to writing back and waiting
8	* upon dirty inodes against superblocks, and writing back dirty
9	* pages against inodes. ie: data writeback. Writeout of the
10	* inode itself is not handled here.
11	*
12	* 10Apr2002 Andrew Morton
13	* Split out of fs/inode.c
14	* Additions for address_space-based writeback
15	*/
16
17	#include <linux/kernel.h>
18	#include <linux/export.h>
19	#include <linux/spinlock.h>
20	#include <linux/slab.h>
21	#include <linux/sched.h>
22	#include <linux/fs.h>
23	#include <linux/mm.h>
24	#include <linux/pagemap.h>
25	#include <linux/kthread.h>
26	#include <linux/writeback.h>
27	#include <linux/blkdev.h>
28	#include <linux/backing-dev.h>
29	#include <linux/tracepoint.h>
30	#include <linux/device.h>
31	#include <linux/memcontrol.h>
32	#include "internal.h"
33
34	/*
35	* 4MB minimal write chunk size
36	*/
37	#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_SHIFT - 10))
38
39	/*
40	* Passed into wb_writeback(), essentially a subset of writeback_control
41	*/
42	struct wb_writeback_work {
43	long nr_pages;
44	struct super_block *sb;
45	enum writeback_sync_modes sync_mode;
46	unsigned int tagged_writepages:1;
47	unsigned int for_kupdate:1;
48	unsigned int range_cyclic:1;
49	unsigned int for_background:1;
50	unsigned int for_sync:1; /* sync(2) WB_SYNC_ALL writeback */
51	unsigned int auto_free:1; /* free on completion */
52	enum wb_reason reason; /* why was writeback initiated? */
53
54	struct list_head list; /* pending work list */
55	struct wb_completion *done; /* set if the caller waits */
56	};
57
58	/*
59	* If an inode is constantly having its pages dirtied, but then the
60	* updates stop dirtytime_expire_interval seconds in the past, it's
61	* possible for the worst case time between when an inode has its
62	* timestamps updated and when they finally get written out to be two
63	* dirtytime_expire_intervals. We set the default to 12 hours (in
64	* seconds), which means most of the time inodes will have their
65	* timestamps written to disk after 12 hours, but in the worst case a
66	* few inodes might not their timestamps updated for 24 hours.
67	*/
68	unsigned int dirtytime_expire_interval = 12 * 60 * 60;
69
70	static inline struct inode *wb_inode(struct list_head *head)
71	{
72	return list_entry(head, struct inode, i_io_list);
73	}
74
75	/*
76	* Include the creation of the trace points after defining the
77	* wb_writeback_work structure and inline functions so that the definition
78	* remains local to this file.
79	*/
80	#define CREATE_TRACE_POINTS
81	#include <trace/events/writeback.h>
82
83	EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
84
85	static bool wb_io_lists_populated(struct bdi_writeback *wb)
86	{
87	if (wb_has_dirty_io(wb)) {
88	return false;
89	} else {
90	set_bit(nr: WB_has_dirty_io, addr: &wb->state);
91	WARN_ON_ONCE(!wb->avg_write_bandwidth);
92	atomic_long_add(i: wb->avg_write_bandwidth,
93	v: &wb->bdi->tot_write_bandwidth);
94	return true;
95	}
96	}
97
98	static void wb_io_lists_depopulated(struct bdi_writeback *wb)
99	{
100	if (wb_has_dirty_io(wb) && list_empty(head: &wb->b_dirty) &&
101	list_empty(head: &wb->b_io) && list_empty(head: &wb->b_more_io)) {
102	clear_bit(nr: WB_has_dirty_io, addr: &wb->state);
103	WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
104	&wb->bdi->tot_write_bandwidth) < 0);
105	}
106	}
107
108	/**
109	* inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
110	* @inode: inode to be moved
111	* @wb: target bdi_writeback
112	* @head: one of @wb->b_{dirty|io|more_io|dirty_time}
113	*
114	* Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
115	* Returns %true if @inode is the first occupant of the !dirty_time IO
116	* lists; otherwise, %false.
117	*/
118	static bool inode_io_list_move_locked(struct inode *inode,
119	struct bdi_writeback *wb,
120	struct list_head *head)
121	{
122	assert_spin_locked(&wb->list_lock);
123	assert_spin_locked(&inode->i_lock);
124	WARN_ON_ONCE(inode->i_state & I_FREEING);
125
126	list_move(list: &inode->i_io_list, head);
127
128	/* dirty_time doesn't count as dirty_io until expiration */
129	if (head != &wb->b_dirty_time)
130	return wb_io_lists_populated(wb);
131
132	wb_io_lists_depopulated(wb);
133	return false;
134	}
135
136	static void wb_wakeup(struct bdi_writeback *wb)
137	{
138	spin_lock_irq(lock: &wb->work_lock);
139	if (test_bit(WB_registered, &wb->state))
140	mod_delayed_work(wq: bdi_wq, dwork: &wb->dwork, delay: 0);
141	spin_unlock_irq(lock: &wb->work_lock);
142	}
143
144	static void finish_writeback_work(struct bdi_writeback *wb,
145	struct wb_writeback_work *work)
146	{
147	struct wb_completion *done = work->done;
148
149	if (work->auto_free)
150	kfree(objp: work);
151	if (done) {
152	wait_queue_head_t *waitq = done->waitq;
153
154	/* @done can't be accessed after the following dec */
155	if (atomic_dec_and_test(v: &done->cnt))
156	wake_up_all(waitq);
157	}
158	}
159
160	static void wb_queue_work(struct bdi_writeback *wb,
161	struct wb_writeback_work *work)
162	{
163	trace_writeback_queue(wb, work);
164
165	if (work->done)
166	atomic_inc(v: &work->done->cnt);
167
168	spin_lock_irq(lock: &wb->work_lock);
169
170	if (test_bit(WB_registered, &wb->state)) {
171	list_add_tail(new: &work->list, head: &wb->work_list);
172	mod_delayed_work(wq: bdi_wq, dwork: &wb->dwork, delay: 0);
173	} else
174	finish_writeback_work(wb, work);
175
176	spin_unlock_irq(lock: &wb->work_lock);
177	}
178
179	/**
180	* wb_wait_for_completion - wait for completion of bdi_writeback_works
181	* @done: target wb_completion
182	*
183	* Wait for one or more work items issued to @bdi with their ->done field
184	* set to @done, which should have been initialized with
185	* DEFINE_WB_COMPLETION(). This function returns after all such work items
186	* are completed. Work items which are waited upon aren't freed
187	* automatically on completion.
188	*/
189	void wb_wait_for_completion(struct wb_completion *done)
190	{
191	atomic_dec(v: &done->cnt); /* put down the initial count */
192	wait_event(*done->waitq, !atomic_read(&done->cnt));
193	}
194
195	#ifdef CONFIG_CGROUP_WRITEBACK
196
197	/*
198	* Parameters for foreign inode detection, see wbc_detach_inode() to see
199	* how they're used.
200	*
201	* These paramters are inherently heuristical as the detection target
202	* itself is fuzzy. All we want to do is detaching an inode from the
203	* current owner if it's being written to by some other cgroups too much.
204	*
205	* The current cgroup writeback is built on the assumption that multiple
206	* cgroups writing to the same inode concurrently is very rare and a mode
207	* of operation which isn't well supported. As such, the goal is not
208	* taking too long when a different cgroup takes over an inode while
209	* avoiding too aggressive flip-flops from occasional foreign writes.
210	*
211	* We record, very roughly, 2s worth of IO time history and if more than
212	* half of that is foreign, trigger the switch. The recording is quantized
213	* to 16 slots. To avoid tiny writes from swinging the decision too much,
214	* writes smaller than 1/8 of avg size are ignored.
215	*/
216	#define WB_FRN_TIME_SHIFT 13 /* 1s = 2^13, upto 8 secs w/ 16bit */
217	#define WB_FRN_TIME_AVG_SHIFT 3 /* avg = avg * 7/8 + new * 1/8 */
218	#define WB_FRN_TIME_CUT_DIV 8 /* ignore rounds < avg / 8 */
219	#define WB_FRN_TIME_PERIOD (2 * (1 << WB_FRN_TIME_SHIFT)) /* 2s */
220
221	#define WB_FRN_HIST_SLOTS 16 /* inode->i_wb_frn_history is 16bit */
222	#define WB_FRN_HIST_UNIT (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
223	/* each slot's duration is 2s / 16 */
224	#define WB_FRN_HIST_THR_SLOTS (WB_FRN_HIST_SLOTS / 2)
225	/* if foreign slots >= 8, switch */
226	#define WB_FRN_HIST_MAX_SLOTS (WB_FRN_HIST_THR_SLOTS / 2 + 1)
227	/* one round can affect upto 5 slots */
228	#define WB_FRN_MAX_IN_FLIGHT 1024 /* don't queue too many concurrently */
229
230	/*
231	* Maximum inodes per isw. A specific value has been chosen to make
232	* struct inode_switch_wbs_context fit into 1024 bytes kmalloc.
233	*/
234	#define WB_MAX_INODES_PER_ISW ((1024UL - sizeof(struct inode_switch_wbs_context)) \
235	/ sizeof(struct inode *))
236
237	static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
238	static struct workqueue_struct *isw_wq;
239
240	void __inode_attach_wb(struct inode *inode, struct folio *folio)
241	{
242	struct backing_dev_info *bdi = inode_to_bdi(inode);
243	struct bdi_writeback *wb = NULL;
244
245	if (inode_cgwb_enabled(inode)) {
246	struct cgroup_subsys_state *memcg_css;
247
248	if (folio) {
249	memcg_css = mem_cgroup_css_from_folio(folio);
250	wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
251	} else {
252	/* must pin memcg_css, see wb_get_create() */
253	memcg_css = task_get_css(current, subsys_id: memory_cgrp_id);
254	wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
255	css_put(css: memcg_css);
256	}
257	}
258
259	if (!wb)
260	wb = &bdi->wb;
261
262	/*
263	* There may be multiple instances of this function racing to
264	* update the same inode. Use cmpxchg() to tell the winner.
265	*/
266	if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
267	wb_put(wb);
268	}
269	EXPORT_SYMBOL_GPL(__inode_attach_wb);
270
271	/**
272	* inode_cgwb_move_to_attached - put the inode onto wb->b_attached list
273	* @inode: inode of interest with i_lock held
274	* @wb: target bdi_writeback
275	*
276	* Remove the inode from wb's io lists and if necessarily put onto b_attached
277	* list. Only inodes attached to cgwb's are kept on this list.
278	*/
279	static void inode_cgwb_move_to_attached(struct inode *inode,
280	struct bdi_writeback *wb)
281	{
282	assert_spin_locked(&wb->list_lock);
283	assert_spin_locked(&inode->i_lock);
284	WARN_ON_ONCE(inode->i_state & I_FREEING);
285
286	inode->i_state &= ~I_SYNC_QUEUED;
287	if (wb != &wb->bdi->wb)
288	list_move(list: &inode->i_io_list, head: &wb->b_attached);
289	else
290	list_del_init(entry: &inode->i_io_list);
291	wb_io_lists_depopulated(wb);
292	}
293
294	/**
295	* locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
296	* @inode: inode of interest with i_lock held
297	*
298	* Returns @inode's wb with its list_lock held. @inode->i_lock must be
299	* held on entry and is released on return. The returned wb is guaranteed
300	* to stay @inode's associated wb until its list_lock is released.
301	*/
302	static struct bdi_writeback *
303	locked_inode_to_wb_and_lock_list(struct inode *inode)
304	__releases(&inode->i_lock)
305	__acquires(&wb->list_lock)
306	{
307	while (true) {
308	struct bdi_writeback *wb = inode_to_wb(inode);
309
310	/*
311	* inode_to_wb() association is protected by both
312	* @inode->i_lock and @wb->list_lock but list_lock nests
313	* outside i_lock. Drop i_lock and verify that the
314	* association hasn't changed after acquiring list_lock.
315	*/
316	wb_get(wb);
317	spin_unlock(lock: &inode->i_lock);
318	spin_lock(lock: &wb->list_lock);
319
320	/* i_wb may have changed inbetween, can't use inode_to_wb() */
321	if (likely(wb == inode->i_wb)) {
322	wb_put(wb); /* @inode already has ref */
323	return wb;
324	}
325
326	spin_unlock(lock: &wb->list_lock);
327	wb_put(wb);
328	cpu_relax();
329	spin_lock(lock: &inode->i_lock);
330	}
331	}
332
333	/**
334	* inode_to_wb_and_lock_list - determine an inode's wb and lock it
335	* @inode: inode of interest
336	*
337	* Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
338	* on entry.
339	*/
340	static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
341	__acquires(&wb->list_lock)
342	{
343	spin_lock(lock: &inode->i_lock);
344	return locked_inode_to_wb_and_lock_list(inode);
345	}
346
347	struct inode_switch_wbs_context {
348	struct rcu_work work;
349
350	/*
351	* Multiple inodes can be switched at once. The switching procedure
352	* consists of two parts, separated by a RCU grace period. To make
353	* sure that the second part is executed for each inode gone through
354	* the first part, all inode pointers are placed into a NULL-terminated
355	* array embedded into struct inode_switch_wbs_context. Otherwise
356	* an inode could be left in a non-consistent state.
357	*/
358	struct bdi_writeback *new_wb;
359	struct inode *inodes[];
360	};
361
362	static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
363	{
364	down_write(sem: &bdi->wb_switch_rwsem);
365	}
366
367	static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
368	{
369	up_write(sem: &bdi->wb_switch_rwsem);
370	}
371
372	static bool inode_do_switch_wbs(struct inode *inode,
373	struct bdi_writeback *old_wb,
374	struct bdi_writeback *new_wb)
375	{
376	struct address_space *mapping = inode->i_mapping;
377	XA_STATE(xas, &mapping->i_pages, 0);
378	struct folio *folio;
379	bool switched = false;
380
381	spin_lock(lock: &inode->i_lock);
382	xa_lock_irq(&mapping->i_pages);
383
384	/*
385	* Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
386	* path owns the inode and we shouldn't modify ->i_io_list.
387	*/
388	if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
389	goto skip_switch;
390
391	trace_inode_switch_wbs(inode, old_wb, new_wb);
392
393	/*
394	* Count and transfer stats. Note that PAGECACHE_TAG_DIRTY points
395	* to possibly dirty folios while PAGECACHE_TAG_WRITEBACK points to
396	* folios actually under writeback.
397	*/
398	xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
399	if (folio_test_dirty(folio)) {
400	long nr = folio_nr_pages(folio);
401	wb_stat_mod(wb: old_wb, item: WB_RECLAIMABLE, amount: -nr);
402	wb_stat_mod(wb: new_wb, item: WB_RECLAIMABLE, amount: nr);
403	}
404	}
405
406	xas_set(xas: &xas, index: 0);
407	xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
408	long nr = folio_nr_pages(folio);
409	WARN_ON_ONCE(!folio_test_writeback(folio));
410	wb_stat_mod(wb: old_wb, item: WB_WRITEBACK, amount: -nr);
411	wb_stat_mod(wb: new_wb, item: WB_WRITEBACK, amount: nr);
412	}
413
414	if (mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK)) {
415	atomic_dec(v: &old_wb->writeback_inodes);
416	atomic_inc(v: &new_wb->writeback_inodes);
417	}
418
419	wb_get(wb: new_wb);
420
421	/*
422	* Transfer to @new_wb's IO list if necessary. If the @inode is dirty,
423	* the specific list @inode was on is ignored and the @inode is put on
424	* ->b_dirty which is always correct including from ->b_dirty_time.
425	* The transfer preserves @inode->dirtied_when ordering. If the @inode
426	* was clean, it means it was on the b_attached list, so move it onto
427	* the b_attached list of @new_wb.
428	*/
429	if (!list_empty(head: &inode->i_io_list)) {
430	inode->i_wb = new_wb;
431
432	if (inode->i_state & I_DIRTY_ALL) {
433	struct inode *pos;
434
435	list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
436	if (time_after_eq(inode->dirtied_when,
437	pos->dirtied_when))
438	break;
439	inode_io_list_move_locked(inode, wb: new_wb,
440	head: pos->i_io_list.prev);
441	} else {
442	inode_cgwb_move_to_attached(inode, wb: new_wb);
443	}
444	} else {
445	inode->i_wb = new_wb;
446	}
447
448	/* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
449	inode->i_wb_frn_winner = 0;
450	inode->i_wb_frn_avg_time = 0;
451	inode->i_wb_frn_history = 0;
452	switched = true;
453	skip_switch:
454	/*
455	* Paired with load_acquire in unlocked_inode_to_wb_begin() and
456	* ensures that the new wb is visible if they see !I_WB_SWITCH.
457	*/
458	smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
459
460	xa_unlock_irq(&mapping->i_pages);
461	spin_unlock(lock: &inode->i_lock);
462
463	return switched;
464	}
465
466	static void inode_switch_wbs_work_fn(struct work_struct *work)
467	{
468	struct inode_switch_wbs_context *isw =
469	container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
470	struct backing_dev_info *bdi = inode_to_bdi(inode: isw->inodes[0]);
471	struct bdi_writeback *old_wb = isw->inodes[0]->i_wb;
472	struct bdi_writeback *new_wb = isw->new_wb;
473	unsigned long nr_switched = 0;
474	struct inode **inodep;
475
476	/*
477	* If @inode switches cgwb membership while sync_inodes_sb() is
478	* being issued, sync_inodes_sb() might miss it. Synchronize.
479	*/
480	down_read(sem: &bdi->wb_switch_rwsem);
481
482	/*
483	* By the time control reaches here, RCU grace period has passed
484	* since I_WB_SWITCH assertion and all wb stat update transactions
485	* between unlocked_inode_to_wb_begin/end() are guaranteed to be
486	* synchronizing against the i_pages lock.
487	*
488	* Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
489	* gives us exclusion against all wb related operations on @inode
490	* including IO list manipulations and stat updates.
491	*/
492	if (old_wb < new_wb) {
493	spin_lock(lock: &old_wb->list_lock);
494	spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
495	} else {
496	spin_lock(lock: &new_wb->list_lock);
497	spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
498	}
499
500	for (inodep = isw->inodes; *inodep; inodep++) {
501	WARN_ON_ONCE((*inodep)->i_wb != old_wb);
502	if (inode_do_switch_wbs(inode: *inodep, old_wb, new_wb))
503	nr_switched++;
504	}
505
506	spin_unlock(lock: &new_wb->list_lock);
507	spin_unlock(lock: &old_wb->list_lock);
508
509	up_read(sem: &bdi->wb_switch_rwsem);
510
511	if (nr_switched) {
512	wb_wakeup(wb: new_wb);
513	wb_put_many(wb: old_wb, nr: nr_switched);
514	}
515
516	for (inodep = isw->inodes; *inodep; inodep++)
517	iput(*inodep);
518	wb_put(wb: new_wb);
519	kfree(objp: isw);
520	atomic_dec(v: &isw_nr_in_flight);
521	}
522
523	static bool inode_prepare_wbs_switch(struct inode *inode,
524	struct bdi_writeback *new_wb)
525	{
526	/*
527	* Paired with smp_mb() in cgroup_writeback_umount().
528	* isw_nr_in_flight must be increased before checking SB_ACTIVE and
529	* grabbing an inode, otherwise isw_nr_in_flight can be observed as 0
530	* in cgroup_writeback_umount() and the isw_wq will be not flushed.
531	*/
532	smp_mb();
533
534	if (IS_DAX(inode))
535	return false;
536
537	/* while holding I_WB_SWITCH, no one else can update the association */
538	spin_lock(lock: &inode->i_lock);
539	if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
540	inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
541	inode_to_wb(inode) == new_wb) {
542	spin_unlock(lock: &inode->i_lock);
543	return false;
544	}
545	inode->i_state |= I_WB_SWITCH;
546	__iget(inode);
547	spin_unlock(lock: &inode->i_lock);
548
549	return true;
550	}
551
552	/**
553	* inode_switch_wbs - change the wb association of an inode
554	* @inode: target inode
555	* @new_wb_id: ID of the new wb
556	*
557	* Switch @inode's wb association to the wb identified by @new_wb_id. The
558	* switching is performed asynchronously and may fail silently.
559	*/
560	static void inode_switch_wbs(struct inode *inode, int new_wb_id)
561	{
562	struct backing_dev_info *bdi = inode_to_bdi(inode);
563	struct cgroup_subsys_state *memcg_css;
564	struct inode_switch_wbs_context *isw;
565
566	/* noop if seems to be already in progress */
567	if (inode->i_state & I_WB_SWITCH)
568	return;
569
570	/* avoid queueing a new switch if too many are already in flight */
571	if (atomic_read(v: &isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
572	return;
573
574	isw = kzalloc(struct_size(isw, inodes, 2), GFP_ATOMIC);
575	if (!isw)
576	return;
577
578	atomic_inc(v: &isw_nr_in_flight);
579
580	/* find and pin the new wb */
581	rcu_read_lock();
582	memcg_css = css_from_id(id: new_wb_id, ss: &memory_cgrp_subsys);
583	if (memcg_css && !css_tryget(css: memcg_css))
584	memcg_css = NULL;
585	rcu_read_unlock();
586	if (!memcg_css)
587	goto out_free;
588
589	isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
590	css_put(css: memcg_css);
591	if (!isw->new_wb)
592	goto out_free;
593
594	if (!inode_prepare_wbs_switch(inode, new_wb: isw->new_wb))
595	goto out_free;
596
597	isw->inodes[0] = inode;
598
599	/*
600	* In addition to synchronizing among switchers, I_WB_SWITCH tells
601	* the RCU protected stat update paths to grab the i_page
602	* lock so that stat transfer can synchronize against them.
603	* Let's continue after I_WB_SWITCH is guaranteed to be visible.
604	*/
605	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
606	queue_rcu_work(wq: isw_wq, rwork: &isw->work);
607	return;
608
609	out_free:
610	atomic_dec(v: &isw_nr_in_flight);
611	if (isw->new_wb)
612	wb_put(wb: isw->new_wb);
613	kfree(objp: isw);
614	}
615
616	static bool isw_prepare_wbs_switch(struct inode_switch_wbs_context *isw,
617	struct list_head *list, int *nr)
618	{
619	struct inode *inode;
620
621	list_for_each_entry(inode, list, i_io_list) {
622	if (!inode_prepare_wbs_switch(inode, new_wb: isw->new_wb))
623	continue;
624
625	isw->inodes[*nr] = inode;
626	(*nr)++;
627
628	if (*nr >= WB_MAX_INODES_PER_ISW - 1)
629	return true;
630	}
631	return false;
632	}
633
634	/**
635	* cleanup_offline_cgwb - detach associated inodes
636	* @wb: target wb
637	*
638	* Switch all inodes attached to @wb to a nearest living ancestor's wb in order
639	* to eventually release the dying @wb. Returns %true if not all inodes were
640	* switched and the function has to be restarted.
641	*/
642	bool cleanup_offline_cgwb(struct bdi_writeback *wb)
643	{
644	struct cgroup_subsys_state *memcg_css;
645	struct inode_switch_wbs_context *isw;
646	int nr;
647	bool restart = false;
648
649	isw = kzalloc(struct_size(isw, inodes, WB_MAX_INODES_PER_ISW),
650	GFP_KERNEL);
651	if (!isw)
652	return restart;
653
654	atomic_inc(v: &isw_nr_in_flight);
655
656	for (memcg_css = wb->memcg_css->parent; memcg_css;
657	memcg_css = memcg_css->parent) {
658	isw->new_wb = wb_get_create(bdi: wb->bdi, memcg_css, GFP_KERNEL);
659	if (isw->new_wb)
660	break;
661	}
662	if (unlikely(!isw->new_wb))
663	isw->new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
664
665	nr = 0;
666	spin_lock(lock: &wb->list_lock);
667	/*
668	* In addition to the inodes that have completed writeback, also switch
669	* cgwbs for those inodes only with dirty timestamps. Otherwise, those
670	* inodes won't be written back for a long time when lazytime is
671	* enabled, and thus pinning the dying cgwbs. It won't break the
672	* bandwidth restrictions, as writeback of inode metadata is not
673	* accounted for.
674	*/
675	restart = isw_prepare_wbs_switch(isw, list: &wb->b_attached, nr: &nr);
676	if (!restart)
677	restart = isw_prepare_wbs_switch(isw, list: &wb->b_dirty_time, nr: &nr);
678	spin_unlock(lock: &wb->list_lock);
679
680	/* no attached inodes? bail out */
681	if (nr == 0) {
682	atomic_dec(v: &isw_nr_in_flight);
683	wb_put(wb: isw->new_wb);
684	kfree(objp: isw);
685	return restart;
686	}
687
688	/*
689	* In addition to synchronizing among switchers, I_WB_SWITCH tells
690	* the RCU protected stat update paths to grab the i_page
691	* lock so that stat transfer can synchronize against them.
692	* Let's continue after I_WB_SWITCH is guaranteed to be visible.
693	*/
694	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
695	queue_rcu_work(wq: isw_wq, rwork: &isw->work);
696
697	return restart;
698	}
699
700	/**
701	* wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
702	* @wbc: writeback_control of interest
703	* @inode: target inode
704	*
705	* @inode is locked and about to be written back under the control of @wbc.
706	* Record @inode's writeback context into @wbc and unlock the i_lock. On
707	* writeback completion, wbc_detach_inode() should be called. This is used
708	* to track the cgroup writeback context.
709	*/
710	void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
711	struct inode *inode)
712	{
713	if (!inode_cgwb_enabled(inode)) {
714	spin_unlock(lock: &inode->i_lock);
715	return;
716	}
717
718	wbc->wb = inode_to_wb(inode);
719	wbc->inode = inode;
720
721	wbc->wb_id = wbc->wb->memcg_css->id;
722	wbc->wb_lcand_id = inode->i_wb_frn_winner;
723	wbc->wb_tcand_id = 0;
724	wbc->wb_bytes = 0;
725	wbc->wb_lcand_bytes = 0;
726	wbc->wb_tcand_bytes = 0;
727
728	wb_get(wb: wbc->wb);
729	spin_unlock(lock: &inode->i_lock);
730
731	/*
732	* A dying wb indicates that either the blkcg associated with the
733	* memcg changed or the associated memcg is dying. In the first
734	* case, a replacement wb should already be available and we should
735	* refresh the wb immediately. In the second case, trying to
736	* refresh will keep failing.
737	*/
738	if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
739	inode_switch_wbs(inode, new_wb_id: wbc->wb_id);
740	}
741	EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
742
743	/**
744	* wbc_detach_inode - disassociate wbc from inode and perform foreign detection
745	* @wbc: writeback_control of the just finished writeback
746	*
747	* To be called after a writeback attempt of an inode finishes and undoes
748	* wbc_attach_and_unlock_inode(). Can be called under any context.
749	*
750	* As concurrent write sharing of an inode is expected to be very rare and
751	* memcg only tracks page ownership on first-use basis severely confining
752	* the usefulness of such sharing, cgroup writeback tracks ownership
753	* per-inode. While the support for concurrent write sharing of an inode
754	* is deemed unnecessary, an inode being written to by different cgroups at
755	* different points in time is a lot more common, and, more importantly,
756	* charging only by first-use can too readily lead to grossly incorrect
757	* behaviors (single foreign page can lead to gigabytes of writeback to be
758	* incorrectly attributed).
759	*
760	* To resolve this issue, cgroup writeback detects the majority dirtier of
761	* an inode and transfers the ownership to it. To avoid unnecessary
762	* oscillation, the detection mechanism keeps track of history and gives
763	* out the switch verdict only if the foreign usage pattern is stable over
764	* a certain amount of time and/or writeback attempts.
765	*
766	* On each writeback attempt, @wbc tries to detect the majority writer
767	* using Boyer-Moore majority vote algorithm. In addition to the byte
768	* count from the majority voting, it also counts the bytes written for the
769	* current wb and the last round's winner wb (max of last round's current
770	* wb, the winner from two rounds ago, and the last round's majority
771	* candidate). Keeping track of the historical winner helps the algorithm
772	* to semi-reliably detect the most active writer even when it's not the
773	* absolute majority.
774	*
775	* Once the winner of the round is determined, whether the winner is
776	* foreign or not and how much IO time the round consumed is recorded in
777	* inode->i_wb_frn_history. If the amount of recorded foreign IO time is
778	* over a certain threshold, the switch verdict is given.
779	*/
780	void wbc_detach_inode(struct writeback_control *wbc)
781	{
782	struct bdi_writeback *wb = wbc->wb;
783	struct inode *inode = wbc->inode;
784	unsigned long avg_time, max_bytes, max_time;
785	u16 history;
786	int max_id;
787
788	if (!wb)
789	return;
790
791	history = inode->i_wb_frn_history;
792	avg_time = inode->i_wb_frn_avg_time;
793
794	/* pick the winner of this round */
795	if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
796	wbc->wb_bytes >= wbc->wb_tcand_bytes) {
797	max_id = wbc->wb_id;
798	max_bytes = wbc->wb_bytes;
799	} else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
800	max_id = wbc->wb_lcand_id;
801	max_bytes = wbc->wb_lcand_bytes;
802	} else {
803	max_id = wbc->wb_tcand_id;
804	max_bytes = wbc->wb_tcand_bytes;
805	}
806
807	/*
808	* Calculate the amount of IO time the winner consumed and fold it
809	* into the running average kept per inode. If the consumed IO
810	* time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
811	* deciding whether to switch or not. This is to prevent one-off
812	* small dirtiers from skewing the verdict.
813	*/
814	max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
815	wb->avg_write_bandwidth);
816	if (avg_time)
817	avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
818	(avg_time >> WB_FRN_TIME_AVG_SHIFT);
819	else
820	avg_time = max_time; /* immediate catch up on first run */
821
822	if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
823	int slots;
824
825	/*
826	* The switch verdict is reached if foreign wb's consume
827	* more than a certain proportion of IO time in a
828	* WB_FRN_TIME_PERIOD. This is loosely tracked by 16 slot
829	* history mask where each bit represents one sixteenth of
830	* the period. Determine the number of slots to shift into
831	* history from @max_time.
832	*/
833	slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
834	(unsigned long)WB_FRN_HIST_MAX_SLOTS);
835	history <<= slots;
836	if (wbc->wb_id != max_id)
837	history |= (1U << slots) - 1;
838
839	if (history)
840	trace_inode_foreign_history(inode, wbc, history);
841
842	/*
843	* Switch if the current wb isn't the consistent winner.
844	* If there are multiple closely competing dirtiers, the
845	* inode may switch across them repeatedly over time, which
846	* is okay. The main goal is avoiding keeping an inode on
847	* the wrong wb for an extended period of time.
848	*/
849	if (hweight16(history) > WB_FRN_HIST_THR_SLOTS)
850	inode_switch_wbs(inode, new_wb_id: max_id);
851	}
852
853	/*
854	* Multiple instances of this function may race to update the
855	* following fields but we don't mind occassional inaccuracies.
856	*/
857	inode->i_wb_frn_winner = max_id;
858	inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
859	inode->i_wb_frn_history = history;
860
861	wb_put(wb: wbc->wb);
862	wbc->wb = NULL;
863	}
864	EXPORT_SYMBOL_GPL(wbc_detach_inode);
865
866	/**
867	* wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
868	* @wbc: writeback_control of the writeback in progress
869	* @page: page being written out
870	* @bytes: number of bytes being written out
871	*
872	* @bytes from @page are about to written out during the writeback
873	* controlled by @wbc. Keep the book for foreign inode detection. See
874	* wbc_detach_inode().
875	*/
876	void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
877	size_t bytes)
878	{
879	struct folio *folio;
880	struct cgroup_subsys_state *css;
881	int id;
882
883	/*
884	* pageout() path doesn't attach @wbc to the inode being written
885	* out. This is intentional as we don't want the function to block
886	* behind a slow cgroup. Ultimately, we want pageout() to kick off
887	* regular writeback instead of writing things out itself.
888	*/
889	if (!wbc->wb || wbc->no_cgroup_owner)
890	return;
891
892	folio = page_folio(page);
893	css = mem_cgroup_css_from_folio(folio);
894	/* dead cgroups shouldn't contribute to inode ownership arbitration */
895	if (!(css->flags & CSS_ONLINE))
896	return;
897
898	id = css->id;
899
900	if (id == wbc->wb_id) {
901	wbc->wb_bytes += bytes;
902	return;
903	}
904
905	if (id == wbc->wb_lcand_id)
906	wbc->wb_lcand_bytes += bytes;
907
908	/* Boyer-Moore majority vote algorithm */
909	if (!wbc->wb_tcand_bytes)
910	wbc->wb_tcand_id = id;
911	if (id == wbc->wb_tcand_id)
912	wbc->wb_tcand_bytes += bytes;
913	else
914	wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
915	}
916	EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
917
918	/**
919	* wb_split_bdi_pages - split nr_pages to write according to bandwidth
920	* @wb: target bdi_writeback to split @nr_pages to
921	* @nr_pages: number of pages to write for the whole bdi
922	*
923	* Split @wb's portion of @nr_pages according to @wb's write bandwidth in
924	* relation to the total write bandwidth of all wb's w/ dirty inodes on
925	* @wb->bdi.
926	*/
927	static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
928	{
929	unsigned long this_bw = wb->avg_write_bandwidth;
930	unsigned long tot_bw = atomic_long_read(v: &wb->bdi->tot_write_bandwidth);
931
932	if (nr_pages == LONG_MAX)
933	return LONG_MAX;
934
935	/*
936	* This may be called on clean wb's and proportional distribution
937	* may not make sense, just use the original @nr_pages in those
938	* cases. In general, we wanna err on the side of writing more.
939	*/
940	if (!tot_bw || this_bw >= tot_bw)
941	return nr_pages;
942	else
943	return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
944	}
945
946	/**
947	* bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
948	* @bdi: target backing_dev_info
949	* @base_work: wb_writeback_work to issue
950	* @skip_if_busy: skip wb's which already have writeback in progress
951	*
952	* Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
953	* have dirty inodes. If @base_work->nr_page isn't %LONG_MAX, it's
954	* distributed to the busy wbs according to each wb's proportion in the
955	* total active write bandwidth of @bdi.
956	*/
957	static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
958	struct wb_writeback_work *base_work,
959	bool skip_if_busy)
960	{
961	struct bdi_writeback *last_wb = NULL;
962	struct bdi_writeback *wb = list_entry(&bdi->wb_list,
963	struct bdi_writeback, bdi_node);
964
965	might_sleep();
966	restart:
967	rcu_read_lock();
968	list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
969	DEFINE_WB_COMPLETION(fallback_work_done, bdi);
970	struct wb_writeback_work fallback_work;
971	struct wb_writeback_work *work;
972	long nr_pages;
973
974	if (last_wb) {
975	wb_put(wb: last_wb);
976	last_wb = NULL;
977	}
978
979	/* SYNC_ALL writes out I_DIRTY_TIME too */
980	if (!wb_has_dirty_io(wb) &&
981	(base_work->sync_mode == WB_SYNC_NONE ||
982	list_empty(head: &wb->b_dirty_time)))
983	continue;
984	if (skip_if_busy && writeback_in_progress(wb))
985	continue;
986
987	nr_pages = wb_split_bdi_pages(wb, nr_pages: base_work->nr_pages);
988
989	work = kmalloc(size: sizeof(*work), GFP_ATOMIC);
990	if (work) {
991	*work = *base_work;
992	work->nr_pages = nr_pages;
993	work->auto_free = 1;
994	wb_queue_work(wb, work);
995	continue;
996	}
997
998	/*
999	* If wb_tryget fails, the wb has been shutdown, skip it.
1000	*
1001	* Pin @wb so that it stays on @bdi->wb_list. This allows
1002	* continuing iteration from @wb after dropping and
1003	* regrabbing rcu read lock.
1004	*/
1005	if (!wb_tryget(wb))
1006	continue;
1007
1008	/* alloc failed, execute synchronously using on-stack fallback */
1009	work = &fallback_work;
1010	*work = *base_work;
1011	work->nr_pages = nr_pages;
1012	work->auto_free = 0;
1013	work->done = &fallback_work_done;
1014
1015	wb_queue_work(wb, work);
1016	last_wb = wb;
1017
1018	rcu_read_unlock();
1019	wb_wait_for_completion(done: &fallback_work_done);
1020	goto restart;
1021	}
1022	rcu_read_unlock();
1023
1024	if (last_wb)
1025	wb_put(wb: last_wb);
1026	}
1027
1028	/**
1029	* cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
1030	* @bdi_id: target bdi id
1031	* @memcg_id: target memcg css id
1032	* @reason: reason why some writeback work initiated
1033	* @done: target wb_completion
1034	*
1035	* Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
1036	* with the specified parameters.
1037	*/
1038	int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,
1039	enum wb_reason reason, struct wb_completion *done)
1040	{
1041	struct backing_dev_info *bdi;
1042	struct cgroup_subsys_state *memcg_css;
1043	struct bdi_writeback *wb;
1044	struct wb_writeback_work *work;
1045	unsigned long dirty;
1046	int ret;
1047
1048	/* lookup bdi and memcg */
1049	bdi = bdi_get_by_id(id: bdi_id);
1050	if (!bdi)
1051	return -ENOENT;
1052
1053	rcu_read_lock();
1054	memcg_css = css_from_id(id: memcg_id, ss: &memory_cgrp_subsys);
1055	if (memcg_css && !css_tryget(css: memcg_css))
1056	memcg_css = NULL;
1057	rcu_read_unlock();
1058	if (!memcg_css) {
1059	ret = -ENOENT;
1060	goto out_bdi_put;
1061	}
1062
1063	/*
1064	* And find the associated wb. If the wb isn't there already
1065	* there's nothing to flush, don't create one.
1066	*/
1067	wb = wb_get_lookup(bdi, memcg_css);
1068	if (!wb) {
1069	ret = -ENOENT;
1070	goto out_css_put;
1071	}
1072
1073	/*
1074	* The caller is attempting to write out most of
1075	* the currently dirty pages. Let's take the current dirty page
1076	* count and inflate it by 25% which should be large enough to
1077	* flush out most dirty pages while avoiding getting livelocked by
1078	* concurrent dirtiers.
1079	*
1080	* BTW the memcg stats are flushed periodically and this is best-effort
1081	* estimation, so some potential error is ok.
1082	*/
1083	dirty = memcg_page_state(memcg: mem_cgroup_from_css(css: memcg_css), idx: NR_FILE_DIRTY);
1084	dirty = dirty * 10 / 8;
1085
1086	/* issue the writeback work */
1087	work = kzalloc(size: sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
1088	if (work) {
1089	work->nr_pages = dirty;
1090	work->sync_mode = WB_SYNC_NONE;
1091	work->range_cyclic = 1;
1092	work->reason = reason;
1093	work->done = done;
1094	work->auto_free = 1;
1095	wb_queue_work(wb, work);
1096	ret = 0;
1097	} else {
1098	ret = -ENOMEM;
1099	}
1100
1101	wb_put(wb);
1102	out_css_put:
1103	css_put(css: memcg_css);
1104	out_bdi_put:
1105	bdi_put(bdi);
1106	return ret;
1107	}
1108
1109	/**
1110	* cgroup_writeback_umount - flush inode wb switches for umount
1111	*
1112	* This function is called when a super_block is about to be destroyed and
1113	* flushes in-flight inode wb switches. An inode wb switch goes through
1114	* RCU and then workqueue, so the two need to be flushed in order to ensure
1115	* that all previously scheduled switches are finished. As wb switches are
1116	* rare occurrences and synchronize_rcu() can take a while, perform
1117	* flushing iff wb switches are in flight.
1118	*/
1119	void cgroup_writeback_umount(void)
1120	{
1121	/*
1122	* SB_ACTIVE should be reliably cleared before checking
1123	* isw_nr_in_flight, see generic_shutdown_super().
1124	*/
1125	smp_mb();
1126
1127	if (atomic_read(v: &isw_nr_in_flight)) {
1128	/*
1129	* Use rcu_barrier() to wait for all pending callbacks to
1130	* ensure that all in-flight wb switches are in the workqueue.
1131	*/
1132	rcu_barrier();
1133	flush_workqueue(isw_wq);
1134	}
1135	}
1136
1137	static int __init cgroup_writeback_init(void)
1138	{
1139	isw_wq = alloc_workqueue(fmt: "inode_switch_wbs", flags: 0, max_active: 0);
1140	if (!isw_wq)
1141	return -ENOMEM;
1142	return 0;
1143	}
1144	fs_initcall(cgroup_writeback_init);
1145
1146	#else /* CONFIG_CGROUP_WRITEBACK */
1147
1148	static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1149	static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1150
1151	static void inode_cgwb_move_to_attached(struct inode *inode,
1152	struct bdi_writeback *wb)
1153	{
1154	assert_spin_locked(&wb->list_lock);
1155	assert_spin_locked(&inode->i_lock);
1156	WARN_ON_ONCE(inode->i_state & I_FREEING);
1157
1158	inode->i_state &= ~I_SYNC_QUEUED;
1159	list_del_init(&inode->i_io_list);
1160	wb_io_lists_depopulated(wb);
1161	}
1162
1163	static struct bdi_writeback *
1164	locked_inode_to_wb_and_lock_list(struct inode *inode)
1165	__releases(&inode->i_lock)
1166	__acquires(&wb->list_lock)
1167	{
1168	struct bdi_writeback *wb = inode_to_wb(inode);
1169
1170	spin_unlock(&inode->i_lock);
1171	spin_lock(&wb->list_lock);
1172	return wb;
1173	}
1174
1175	static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
1176	__acquires(&wb->list_lock)
1177	{
1178	struct bdi_writeback *wb = inode_to_wb(inode);
1179
1180	spin_lock(&wb->list_lock);
1181	return wb;
1182	}
1183
1184	static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
1185	{
1186	return nr_pages;
1187	}
1188
1189	static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
1190	struct wb_writeback_work *base_work,
1191	bool skip_if_busy)
1192	{
1193	might_sleep();
1194
1195	if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
1196	base_work->auto_free = 0;
1197	wb_queue_work(&bdi->wb, base_work);
1198	}
1199	}
1200
1201	#endif /* CONFIG_CGROUP_WRITEBACK */
1202
1203	/*
1204	* Add in the number of potentially dirty inodes, because each inode
1205	* write can dirty pagecache in the underlying blockdev.
1206	*/
1207	static unsigned long get_nr_dirty_pages(void)
1208	{
1209	return global_node_page_state(item: NR_FILE_DIRTY) +
1210	get_nr_dirty_inodes();
1211	}
1212
1213	static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
1214	{
1215	if (!wb_has_dirty_io(wb))
1216	return;
1217
1218	/*
1219	* All callers of this function want to start writeback of all
1220	* dirty pages. Places like vmscan can call this at a very
1221	* high frequency, causing pointless allocations of tons of
1222	* work items and keeping the flusher threads busy retrieving
1223	* that work. Ensure that we only allow one of them pending and
1224	* inflight at the time.
1225	*/
1226	if (test_bit(WB_start_all, &wb->state) ||
1227	test_and_set_bit(nr: WB_start_all, addr: &wb->state))
1228	return;
1229
1230	wb->start_all_reason = reason;
1231	wb_wakeup(wb);
1232	}
1233
1234	/**
1235	* wb_start_background_writeback - start background writeback
1236	* @wb: bdi_writback to write from
1237	*
1238	* Description:
1239	* This makes sure WB_SYNC_NONE background writeback happens. When
1240	* this function returns, it is only guaranteed that for given wb
1241	* some IO is happening if we are over background dirty threshold.
1242	* Caller need not hold sb s_umount semaphore.
1243	*/
1244	void wb_start_background_writeback(struct bdi_writeback *wb)
1245	{
1246	/*
1247	* We just wake up the flusher thread. It will perform background
1248	* writeback as soon as there is no other work to do.
1249	*/
1250	trace_writeback_wake_background(wb);
1251	wb_wakeup(wb);
1252	}
1253
1254	/*
1255	* Remove the inode from the writeback list it is on.
1256	*/
1257	void inode_io_list_del(struct inode *inode)
1258	{
1259	struct bdi_writeback *wb;
1260
1261	wb = inode_to_wb_and_lock_list(inode);
1262	spin_lock(lock: &inode->i_lock);
1263
1264	inode->i_state &= ~I_SYNC_QUEUED;
1265	list_del_init(entry: &inode->i_io_list);
1266	wb_io_lists_depopulated(wb);
1267
1268	spin_unlock(lock: &inode->i_lock);
1269	spin_unlock(lock: &wb->list_lock);
1270	}
1271	EXPORT_SYMBOL(inode_io_list_del);
1272
1273	/*
1274	* mark an inode as under writeback on the sb
1275	*/
1276	void sb_mark_inode_writeback(struct inode *inode)
1277	{
1278	struct super_block *sb = inode->i_sb;
1279	unsigned long flags;
1280
1281	if (list_empty(head: &inode->i_wb_list)) {
1282	spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1283	if (list_empty(head: &inode->i_wb_list)) {
1284	list_add_tail(new: &inode->i_wb_list, head: &sb->s_inodes_wb);
1285	trace_sb_mark_inode_writeback(inode);
1286	}
1287	spin_unlock_irqrestore(lock: &sb->s_inode_wblist_lock, flags);
1288	}
1289	}
1290
1291	/*
1292	* clear an inode as under writeback on the sb
1293	*/
1294	void sb_clear_inode_writeback(struct inode *inode)
1295	{
1296	struct super_block *sb = inode->i_sb;
1297	unsigned long flags;
1298
1299	if (!list_empty(head: &inode->i_wb_list)) {
1300	spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1301	if (!list_empty(head: &inode->i_wb_list)) {
1302	list_del_init(entry: &inode->i_wb_list);
1303	trace_sb_clear_inode_writeback(inode);
1304	}
1305	spin_unlock_irqrestore(lock: &sb->s_inode_wblist_lock, flags);
1306	}
1307	}
1308
1309	/*
1310	* Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1311	* furthest end of its superblock's dirty-inode list.
1312	*
1313	* Before stamping the inode's ->dirtied_when, we check to see whether it is
1314	* already the most-recently-dirtied inode on the b_dirty list. If that is
1315	* the case then the inode must have been redirtied while it was being written
1316	* out and we don't reset its dirtied_when.
1317	*/
1318	static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
1319	{
1320	assert_spin_locked(&inode->i_lock);
1321
1322	inode->i_state &= ~I_SYNC_QUEUED;
1323	/*
1324	* When the inode is being freed just don't bother with dirty list
1325	* tracking. Flush worker will ignore this inode anyway and it will
1326	* trigger assertions in inode_io_list_move_locked().
1327	*/
1328	if (inode->i_state & I_FREEING) {
1329	list_del_init(entry: &inode->i_io_list);
1330	wb_io_lists_depopulated(wb);
1331	return;
1332	}
1333	if (!list_empty(head: &wb->b_dirty)) {
1334	struct inode *tail;
1335
1336	tail = wb_inode(head: wb->b_dirty.next);
1337	if (time_before(inode->dirtied_when, tail->dirtied_when))
1338	inode->dirtied_when = jiffies;
1339	}
1340	inode_io_list_move_locked(inode, wb, head: &wb->b_dirty);
1341	}
1342
1343	static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
1344	{
1345	spin_lock(lock: &inode->i_lock);
1346	redirty_tail_locked(inode, wb);
1347	spin_unlock(lock: &inode->i_lock);
1348	}
1349
1350	/*
1351	* requeue inode for re-scanning after bdi->b_io list is exhausted.
1352	*/
1353	static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
1354	{
1355	inode_io_list_move_locked(inode, wb, head: &wb->b_more_io);
1356	}
1357
1358	static void inode_sync_complete(struct inode *inode)
1359	{
1360	inode->i_state &= ~I_SYNC;
1361	/* If inode is clean an unused, put it into LRU now... */
1362	inode_add_lru(inode);
1363	/* Waiters must see I_SYNC cleared before being woken up */
1364	smp_mb();
1365	wake_up_bit(word: &inode->i_state, __I_SYNC);
1366	}
1367
1368	static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1369	{
1370	bool ret = time_after(inode->dirtied_when, t);
1371	#ifndef CONFIG_64BIT
1372	/*
1373	* For inodes being constantly redirtied, dirtied_when can get stuck.
1374	* It _appears_ to be in the future, but is actually in distant past.
1375	* This test is necessary to prevent such wrapped-around relative times
1376	* from permanently stopping the whole bdi writeback.
1377	*/
1378	ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1379	#endif
1380	return ret;
1381	}
1382
1383	/*
1384	* Move expired (dirtied before dirtied_before) dirty inodes from
1385	* @delaying_queue to @dispatch_queue.
1386	*/
1387	static int move_expired_inodes(struct list_head *delaying_queue,
1388	struct list_head *dispatch_queue,
1389	unsigned long dirtied_before)
1390	{
1391	LIST_HEAD(tmp);
1392	struct list_head *pos, *node;
1393	struct super_block *sb = NULL;
1394	struct inode *inode;
1395	int do_sb_sort = 0;
1396	int moved = 0;
1397
1398	while (!list_empty(head: delaying_queue)) {
1399	inode = wb_inode(head: delaying_queue->prev);
1400	if (inode_dirtied_after(inode, t: dirtied_before))
1401	break;
1402	spin_lock(lock: &inode->i_lock);
1403	list_move(list: &inode->i_io_list, head: &tmp);
1404	moved++;
1405	inode->i_state |= I_SYNC_QUEUED;
1406	spin_unlock(lock: &inode->i_lock);
1407	if (sb_is_blkdev_sb(sb: inode->i_sb))
1408	continue;
1409	if (sb && sb != inode->i_sb)
1410	do_sb_sort = 1;
1411	sb = inode->i_sb;
1412	}
1413
1414	/* just one sb in list, splice to dispatch_queue and we're done */
1415	if (!do_sb_sort) {
1416	list_splice(list: &tmp, head: dispatch_queue);
1417	goto out;
1418	}
1419
1420	/*
1421	* Although inode's i_io_list is moved from 'tmp' to 'dispatch_queue',
1422	* we don't take inode->i_lock here because it is just a pointless overhead.
1423	* Inode is already marked as I_SYNC_QUEUED so writeback list handling is
1424	* fully under our control.
1425	*/
1426	while (!list_empty(head: &tmp)) {
1427	sb = wb_inode(head: tmp.prev)->i_sb;
1428	list_for_each_prev_safe(pos, node, &tmp) {
1429	inode = wb_inode(head: pos);
1430	if (inode->i_sb == sb)
1431	list_move(list: &inode->i_io_list, head: dispatch_queue);
1432	}
1433	}
1434	out:
1435	return moved;
1436	}
1437
1438	/*
1439	* Queue all expired dirty inodes for io, eldest first.
1440	* Before
1441	* newly dirtied b_dirty b_io b_more_io
1442	* =============> gf edc BA
1443	* After
1444	* newly dirtied b_dirty b_io b_more_io
1445	* =============> g fBAedc
1446	* |
1447	* +--> dequeue for IO
1448	*/
1449	static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
1450	unsigned long dirtied_before)
1451	{
1452	int moved;
1453	unsigned long time_expire_jif = dirtied_before;
1454
1455	assert_spin_locked(&wb->list_lock);
1456	list_splice_init(list: &wb->b_more_io, head: &wb->b_io);
1457	moved = move_expired_inodes(delaying_queue: &wb->b_dirty, dispatch_queue: &wb->b_io, dirtied_before);
1458	if (!work->for_sync)
1459	time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
1460	moved += move_expired_inodes(delaying_queue: &wb->b_dirty_time, dispatch_queue: &wb->b_io,
1461	dirtied_before: time_expire_jif);
1462	if (moved)
1463	wb_io_lists_populated(wb);
1464	trace_writeback_queue_io(wb, work, dirtied_before, moved);
1465	}
1466
1467	static int write_inode(struct inode *inode, struct writeback_control *wbc)
1468	{
1469	int ret;
1470
1471	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1472	trace_writeback_write_inode_start(inode, wbc);
1473	ret = inode->i_sb->s_op->write_inode(inode, wbc);
1474	trace_writeback_write_inode(inode, wbc);
1475	return ret;
1476	}
1477	return 0;
1478	}
1479
1480	/*
1481	* Wait for writeback on an inode to complete. Called with i_lock held.
1482	* Caller must make sure inode cannot go away when we drop i_lock.
1483	*/
1484	static void __inode_wait_for_writeback(struct inode *inode)
1485	__releases(inode->i_lock)
1486	__acquires(inode->i_lock)
1487	{
1488	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1489	wait_queue_head_t *wqh;
1490
1491	wqh = bit_waitqueue(word: &inode->i_state, __I_SYNC);
1492	while (inode->i_state & I_SYNC) {
1493	spin_unlock(lock: &inode->i_lock);
1494	__wait_on_bit(wq_head: wqh, wbq_entry: &wq, action: bit_wait,
1495	TASK_UNINTERRUPTIBLE);
1496	spin_lock(lock: &inode->i_lock);
1497	}
1498	}
1499
1500	/*
1501	* Wait for writeback on an inode to complete. Caller must have inode pinned.
1502	*/
1503	void inode_wait_for_writeback(struct inode *inode)
1504	{
1505	spin_lock(lock: &inode->i_lock);
1506	__inode_wait_for_writeback(inode);
1507	spin_unlock(lock: &inode->i_lock);
1508	}
1509
1510	/*
1511	* Sleep until I_SYNC is cleared. This function must be called with i_lock
1512	* held and drops it. It is aimed for callers not holding any inode reference
1513	* so once i_lock is dropped, inode can go away.
1514	*/
1515	static void inode_sleep_on_writeback(struct inode *inode)
1516	__releases(inode->i_lock)
1517	{
1518	DEFINE_WAIT(wait);
1519	wait_queue_head_t *wqh = bit_waitqueue(word: &inode->i_state, __I_SYNC);
1520	int sleep;
1521
1522	prepare_to_wait(wq_head: wqh, wq_entry: &wait, TASK_UNINTERRUPTIBLE);
1523	sleep = inode->i_state & I_SYNC;
1524	spin_unlock(lock: &inode->i_lock);
1525	if (sleep)
1526	schedule();
1527	finish_wait(wq_head: wqh, wq_entry: &wait);
1528	}
1529
1530	/*
1531	* Find proper writeback list for the inode depending on its current state and
1532	* possibly also change of its state while we were doing writeback. Here we
1533	* handle things such as livelock prevention or fairness of writeback among
1534	* inodes. This function can be called only by flusher thread - noone else
1535	* processes all inodes in writeback lists and requeueing inodes behind flusher
1536	* thread's back can have unexpected consequences.
1537	*/
1538	static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1539	struct writeback_control *wbc)
1540	{
1541	if (inode->i_state & I_FREEING)
1542	return;
1543
1544	/*
1545	* Sync livelock prevention. Each inode is tagged and synced in one
1546	* shot. If still dirty, it will be redirty_tail()'ed below. Update
1547	* the dirty time to prevent enqueue and sync it again.
1548	*/
1549	if ((inode->i_state & I_DIRTY) &&
1550	(wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1551	inode->dirtied_when = jiffies;
1552
1553	if (wbc->pages_skipped) {
1554	/*
1555	* Writeback is not making progress due to locked buffers.
1556	* Skip this inode for now. Although having skipped pages
1557	* is odd for clean inodes, it can happen for some
1558	* filesystems so handle that gracefully.
1559	*/
1560	if (inode->i_state & I_DIRTY_ALL)
1561	redirty_tail_locked(inode, wb);
1562	else
1563	inode_cgwb_move_to_attached(inode, wb);
1564	return;
1565	}
1566
1567	if (mapping_tagged(mapping: inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1568	/*
1569	* We didn't write back all the pages. nfs_writepages()
1570	* sometimes bales out without doing anything.
1571	*/
1572	if (wbc->nr_to_write <= 0) {
1573	/* Slice used up. Queue for next turn. */
1574	requeue_io(inode, wb);
1575	} else {
1576	/*
1577	* Writeback blocked by something other than
1578	* congestion. Delay the inode for some time to
1579	* avoid spinning on the CPU (100% iowait)
1580	* retrying writeback of the dirty page/inode
1581	* that cannot be performed immediately.
1582	*/
1583	redirty_tail_locked(inode, wb);
1584	}
1585	} else if (inode->i_state & I_DIRTY) {
1586	/*
1587	* Filesystems can dirty the inode during writeback operations,
1588	* such as delayed allocation during submission or metadata
1589	* updates after data IO completion.
1590	*/
1591	redirty_tail_locked(inode, wb);
1592	} else if (inode->i_state & I_DIRTY_TIME) {
1593	inode->dirtied_when = jiffies;
1594	inode_io_list_move_locked(inode, wb, head: &wb->b_dirty_time);
1595	inode->i_state &= ~I_SYNC_QUEUED;
1596	} else {
1597	/* The inode is clean. Remove from writeback lists. */
1598	inode_cgwb_move_to_attached(inode, wb);
1599	}
1600	}
1601
1602	/*
1603	* Write out an inode and its dirty pages (or some of its dirty pages, depending
1604	* on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
1605	*
1606	* This doesn't remove the inode from the writeback list it is on, except
1607	* potentially to move it from b_dirty_time to b_dirty due to timestamp
1608	* expiration. The caller is otherwise responsible for writeback list handling.
1609	*
1610	* The caller is also responsible for setting the I_SYNC flag beforehand and
1611	* calling inode_sync_complete() to clear it afterwards.
1612	*/
1613	static int
1614	__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1615	{
1616	struct address_space *mapping = inode->i_mapping;
1617	long nr_to_write = wbc->nr_to_write;
1618	unsigned dirty;
1619	int ret;
1620
1621	WARN_ON(!(inode->i_state & I_SYNC));
1622
1623	trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1624
1625	ret = do_writepages(mapping, wbc);
1626
1627	/*
1628	* Make sure to wait on the data before writing out the metadata.
1629	* This is important for filesystems that modify metadata on data
1630	* I/O completion. We don't do it for sync(2) writeback because it has a
1631	* separate, external IO completion path and ->sync_fs for guaranteeing
1632	* inode metadata is written back correctly.
1633	*/
1634	if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1635	int err = filemap_fdatawait(mapping);
1636	if (ret == 0)
1637	ret = err;
1638	}
1639
1640	/*
1641	* If the inode has dirty timestamps and we need to write them, call
1642	* mark_inode_dirty_sync() to notify the filesystem about it and to
1643	* change I_DIRTY_TIME into I_DIRTY_SYNC.
1644	*/
1645	if ((inode->i_state & I_DIRTY_TIME) &&
1646	(wbc->sync_mode == WB_SYNC_ALL ||
1647	time_after(jiffies, inode->dirtied_time_when +
1648	dirtytime_expire_interval * HZ))) {
1649	trace_writeback_lazytime(inode);
1650	mark_inode_dirty_sync(inode);
1651	}
1652
1653	/*
1654	* Get and clear the dirty flags from i_state. This needs to be done
1655	* after calling writepages because some filesystems may redirty the
1656	* inode during writepages due to delalloc. It also needs to be done
1657	* after handling timestamp expiration, as that may dirty the inode too.
1658	*/
1659	spin_lock(lock: &inode->i_lock);
1660	dirty = inode->i_state & I_DIRTY;
1661	inode->i_state &= ~dirty;
1662
1663	/*
1664	* Paired with smp_mb() in __mark_inode_dirty(). This allows
1665	* __mark_inode_dirty() to test i_state without grabbing i_lock -
1666	* either they see the I_DIRTY bits cleared or we see the dirtied
1667	* inode.
1668	*
1669	* I_DIRTY_PAGES is always cleared together above even if @mapping
1670	* still has dirty pages. The flag is reinstated after smp_mb() if
1671	* necessary. This guarantees that either __mark_inode_dirty()
1672	* sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1673	*/
1674	smp_mb();
1675
1676	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1677	inode->i_state |= I_DIRTY_PAGES;
1678	else if (unlikely(inode->i_state & I_PINNING_FSCACHE_WB)) {
1679	if (!(inode->i_state & I_DIRTY_PAGES)) {
1680	inode->i_state &= ~I_PINNING_FSCACHE_WB;
1681	wbc->unpinned_fscache_wb = true;
1682	dirty |= I_PINNING_FSCACHE_WB; /* Cause write_inode */
1683	}
1684	}
1685
1686	spin_unlock(lock: &inode->i_lock);
1687
1688	/* Don't write the inode if only I_DIRTY_PAGES was set */
1689	if (dirty & ~I_DIRTY_PAGES) {
1690	int err = write_inode(inode, wbc);
1691	if (ret == 0)
1692	ret = err;
1693	}
1694	wbc->unpinned_fscache_wb = false;
1695	trace_writeback_single_inode(inode, wbc, nr_to_write);
1696	return ret;
1697	}
1698
1699	/*
1700	* Write out an inode's dirty data and metadata on-demand, i.e. separately from
1701	* the regular batched writeback done by the flusher threads in
1702	* writeback_sb_inodes(). @wbc controls various aspects of the write, such as
1703	* whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
1704	*
1705	* To prevent the inode from going away, either the caller must have a reference
1706	* to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
1707	*/
1708	static int writeback_single_inode(struct inode *inode,
1709	struct writeback_control *wbc)
1710	{
1711	struct bdi_writeback *wb;
1712	int ret = 0;
1713
1714	spin_lock(lock: &inode->i_lock);
1715	if (!atomic_read(v: &inode->i_count))
1716	WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1717	else
1718	WARN_ON(inode->i_state & I_WILL_FREE);
1719
1720	if (inode->i_state & I_SYNC) {
1721	/*
1722	* Writeback is already running on the inode. For WB_SYNC_NONE,
1723	* that's enough and we can just return. For WB_SYNC_ALL, we
1724	* must wait for the existing writeback to complete, then do
1725	* writeback again if there's anything left.
1726	*/
1727	if (wbc->sync_mode != WB_SYNC_ALL)
1728	goto out;
1729	__inode_wait_for_writeback(inode);
1730	}
1731	WARN_ON(inode->i_state & I_SYNC);
1732	/*
1733	* If the inode is already fully clean, then there's nothing to do.
1734	*
1735	* For data-integrity syncs we also need to check whether any pages are
1736	* still under writeback, e.g. due to prior WB_SYNC_NONE writeback. If
1737	* there are any such pages, we'll need to wait for them.
1738	*/
1739	if (!(inode->i_state & I_DIRTY_ALL) &&
1740	(wbc->sync_mode != WB_SYNC_ALL ||
1741	!mapping_tagged(mapping: inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1742	goto out;
1743	inode->i_state |= I_SYNC;
1744	wbc_attach_and_unlock_inode(wbc, inode);
1745
1746	ret = __writeback_single_inode(inode, wbc);
1747
1748	wbc_detach_inode(wbc);
1749
1750	wb = inode_to_wb_and_lock_list(inode);
1751	spin_lock(lock: &inode->i_lock);
1752	/*
1753	* If the inode is freeing, its i_io_list shoudn't be updated
1754	* as it can be finally deleted at this moment.
1755	*/
1756	if (!(inode->i_state & I_FREEING)) {
1757	/*
1758	* If the inode is now fully clean, then it can be safely
1759	* removed from its writeback list (if any). Otherwise the
1760	* flusher threads are responsible for the writeback lists.
1761	*/
1762	if (!(inode->i_state & I_DIRTY_ALL))
1763	inode_cgwb_move_to_attached(inode, wb);
1764	else if (!(inode->i_state & I_SYNC_QUEUED)) {
1765	if ((inode->i_state & I_DIRTY))
1766	redirty_tail_locked(inode, wb);
1767	else if (inode->i_state & I_DIRTY_TIME) {
1768	inode->dirtied_when = jiffies;
1769	inode_io_list_move_locked(inode,
1770	wb,
1771	head: &wb->b_dirty_time);
1772	}
1773	}
1774	}
1775
1776	spin_unlock(lock: &wb->list_lock);
1777	inode_sync_complete(inode);
1778	out:
1779	spin_unlock(lock: &inode->i_lock);
1780	return ret;
1781	}
1782
1783	static long writeback_chunk_size(struct bdi_writeback *wb,
1784	struct wb_writeback_work *work)
1785	{
1786	long pages;
1787
1788	/*
1789	* WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1790	* inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1791	* here avoids calling into writeback_inodes_wb() more than once.
1792	*
1793	* The intended call sequence for WB_SYNC_ALL writeback is:
1794	*
1795	* wb_writeback()
1796	* writeback_sb_inodes() <== called only once
1797	* write_cache_pages() <== called once for each inode
1798	* (quickly) tag currently dirty pages
1799	* (maybe slowly) sync all tagged pages
1800	*/
1801	if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1802	pages = LONG_MAX;
1803	else {
1804	pages = min(wb->avg_write_bandwidth / 2,
1805	global_wb_domain.dirty_limit / DIRTY_SCOPE);
1806	pages = min(pages, work->nr_pages);
1807	pages = round_down(pages + MIN_WRITEBACK_PAGES,
1808	MIN_WRITEBACK_PAGES);
1809	}
1810
1811	return pages;
1812	}
1813
1814	/*
1815	* Write a portion of b_io inodes which belong to @sb.
1816	*
1817	* Return the number of pages and/or inodes written.
1818	*
1819	* NOTE! This is called with wb->list_lock held, and will
1820	* unlock and relock that for each inode it ends up doing
1821	* IO for.
1822	*/
1823	static long writeback_sb_inodes(struct super_block *sb,
1824	struct bdi_writeback *wb,
1825	struct wb_writeback_work *work)
1826	{
1827	struct writeback_control wbc = {
1828	.sync_mode = work->sync_mode,
1829	.tagged_writepages = work->tagged_writepages,
1830	.for_kupdate = work->for_kupdate,
1831	.for_background = work->for_background,
1832	.for_sync = work->for_sync,
1833	.range_cyclic = work->range_cyclic,
1834	.range_start = 0,
1835	.range_end = LLONG_MAX,
1836	};
1837	unsigned long start_time = jiffies;
1838	long write_chunk;
1839	long total_wrote = 0; /* count both pages and inodes */
1840
1841	while (!list_empty(head: &wb->b_io)) {
1842	struct inode *inode = wb_inode(head: wb->b_io.prev);
1843	struct bdi_writeback *tmp_wb;
1844	long wrote;
1845
1846	if (inode->i_sb != sb) {
1847	if (work->sb) {
1848	/*
1849	* We only want to write back data for this
1850	* superblock, move all inodes not belonging
1851	* to it back onto the dirty list.
1852	*/
1853	redirty_tail(inode, wb);
1854	continue;
1855	}
1856
1857	/*
1858	* The inode belongs to a different superblock.
1859	* Bounce back to the caller to unpin this and
1860	* pin the next superblock.
1861	*/
1862	break;
1863	}
1864
1865	/*
1866	* Don't bother with new inodes or inodes being freed, first
1867	* kind does not need periodic writeout yet, and for the latter
1868	* kind writeout is handled by the freer.
1869	*/
1870	spin_lock(lock: &inode->i_lock);
1871	if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1872	redirty_tail_locked(inode, wb);
1873	spin_unlock(lock: &inode->i_lock);
1874	continue;
1875	}
1876	if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1877	/*
1878	* If this inode is locked for writeback and we are not
1879	* doing writeback-for-data-integrity, move it to
1880	* b_more_io so that writeback can proceed with the
1881	* other inodes on s_io.
1882	*
1883	* We'll have another go at writing back this inode
1884	* when we completed a full scan of b_io.
1885	*/
1886	requeue_io(inode, wb);
1887	spin_unlock(lock: &inode->i_lock);
1888	trace_writeback_sb_inodes_requeue(inode);
1889	continue;
1890	}
1891	spin_unlock(lock: &wb->list_lock);
1892
1893	/*
1894	* We already requeued the inode if it had I_SYNC set and we
1895	* are doing WB_SYNC_NONE writeback. So this catches only the
1896	* WB_SYNC_ALL case.
1897	*/
1898	if (inode->i_state & I_SYNC) {
1899	/* Wait for I_SYNC. This function drops i_lock... */
1900	inode_sleep_on_writeback(inode);
1901	/* Inode may be gone, start again */
1902	spin_lock(lock: &wb->list_lock);
1903	continue;
1904	}
1905	inode->i_state |= I_SYNC;
1906	wbc_attach_and_unlock_inode(&wbc, inode);
1907
1908	write_chunk = writeback_chunk_size(wb, work);
1909	wbc.nr_to_write = write_chunk;
1910	wbc.pages_skipped = 0;
1911
1912	/*
1913	* We use I_SYNC to pin the inode in memory. While it is set
1914	* evict_inode() will wait so the inode cannot be freed.
1915	*/
1916	__writeback_single_inode(inode, wbc: &wbc);
1917
1918	wbc_detach_inode(&wbc);
1919	work->nr_pages -= write_chunk - wbc.nr_to_write;
1920	wrote = write_chunk - wbc.nr_to_write - wbc.pages_skipped;
1921	wrote = wrote < 0 ? 0 : wrote;
1922	total_wrote += wrote;
1923
1924	if (need_resched()) {
1925	/*
1926	* We're trying to balance between building up a nice
1927	* long list of IOs to improve our merge rate, and
1928	* getting those IOs out quickly for anyone throttling
1929	* in balance_dirty_pages(). cond_resched() doesn't
1930	* unplug, so get our IOs out the door before we
1931	* give up the CPU.
1932	*/
1933	blk_flush_plug(current->plug, async: false);
1934	cond_resched();
1935	}
1936
1937	/*
1938	* Requeue @inode if still dirty. Be careful as @inode may
1939	* have been switched to another wb in the meantime.
1940	*/
1941	tmp_wb = inode_to_wb_and_lock_list(inode);
1942	spin_lock(lock: &inode->i_lock);
1943	if (!(inode->i_state & I_DIRTY_ALL))
1944	total_wrote++;
1945	requeue_inode(inode, wb: tmp_wb, wbc: &wbc);
1946	inode_sync_complete(inode);
1947	spin_unlock(lock: &inode->i_lock);
1948
1949	if (unlikely(tmp_wb != wb)) {
1950	spin_unlock(lock: &tmp_wb->list_lock);
1951	spin_lock(lock: &wb->list_lock);
1952	}
1953
1954	/*
1955	* bail out to wb_writeback() often enough to check
1956	* background threshold and other termination conditions.
1957	*/
1958	if (total_wrote) {
1959	if (time_is_before_jiffies(start_time + HZ / 10UL))
1960	break;
1961	if (work->nr_pages <= 0)
1962	break;
1963	}
1964	}
1965	return total_wrote;
1966	}
1967
1968	static long __writeback_inodes_wb(struct bdi_writeback *wb,
1969	struct wb_writeback_work *work)
1970	{
1971	unsigned long start_time = jiffies;
1972	long wrote = 0;
1973
1974	while (!list_empty(head: &wb->b_io)) {
1975	struct inode *inode = wb_inode(head: wb->b_io.prev);
1976	struct super_block *sb = inode->i_sb;
1977
1978	if (!super_trylock_shared(sb)) {
1979	/*
1980	* super_trylock_shared() may fail consistently due to
1981	* s_umount being grabbed by someone else. Don't use
1982	* requeue_io() to avoid busy retrying the inode/sb.
1983	*/
1984	redirty_tail(inode, wb);
1985	continue;
1986	}
1987	wrote += writeback_sb_inodes(sb, wb, work);
1988	up_read(sem: &sb->s_umount);
1989
1990	/* refer to the same tests at the end of writeback_sb_inodes */
1991	if (wrote) {
1992	if (time_is_before_jiffies(start_time + HZ / 10UL))
1993	break;
1994	if (work->nr_pages <= 0)
1995	break;
1996	}
1997	}
1998	/* Leave any unwritten inodes on b_io */
1999	return wrote;
2000	}
2001
2002	static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
2003	enum wb_reason reason)
2004	{
2005	struct wb_writeback_work work = {
2006	.nr_pages = nr_pages,
2007	.sync_mode = WB_SYNC_NONE,
2008	.range_cyclic = 1,
2009	.reason = reason,
2010	};
2011	struct blk_plug plug;
2012
2013	blk_start_plug(&plug);
2014	spin_lock(lock: &wb->list_lock);
2015	if (list_empty(head: &wb->b_io))
2016	queue_io(wb, work: &work, dirtied_before: jiffies);
2017	__writeback_inodes_wb(wb, work: &work);
2018	spin_unlock(lock: &wb->list_lock);
2019	blk_finish_plug(&plug);
2020
2021	return nr_pages - work.nr_pages;
2022	}
2023
2024	/*
2025	* Explicit flushing or periodic writeback of "old" data.
2026	*
2027	* Define "old": the first time one of an inode's pages is dirtied, we mark the
2028	* dirtying-time in the inode's address_space. So this periodic writeback code
2029	* just walks the superblock inode list, writing back any inodes which are
2030	* older than a specific point in time.
2031	*
2032	* Try to run once per dirty_writeback_interval. But if a writeback event
2033	* takes longer than a dirty_writeback_interval interval, then leave a
2034	* one-second gap.
2035	*
2036	* dirtied_before takes precedence over nr_to_write. So we'll only write back
2037	* all dirty pages if they are all attached to "old" mappings.
2038	*/
2039	static long wb_writeback(struct bdi_writeback *wb,
2040	struct wb_writeback_work *work)
2041	{
2042	long nr_pages = work->nr_pages;
2043	unsigned long dirtied_before = jiffies;
2044	struct inode *inode;
2045	long progress;
2046	struct blk_plug plug;
2047
2048	blk_start_plug(&plug);
2049	for (;;) {
2050	/*
2051	* Stop writeback when nr_pages has been consumed
2052	*/
2053	if (work->nr_pages <= 0)
2054	break;
2055
2056	/*
2057	* Background writeout and kupdate-style writeback may
2058	* run forever. Stop them if there is other work to do
2059	* so that e.g. sync can proceed. They'll be restarted
2060	* after the other works are all done.
2061	*/
2062	if ((work->for_background || work->for_kupdate) &&
2063	!list_empty(head: &wb->work_list))
2064	break;
2065
2066	/*
2067	* For background writeout, stop when we are below the
2068	* background dirty threshold
2069	*/
2070	if (work->for_background && !wb_over_bg_thresh(wb))
2071	break;
2072
2073
2074	spin_lock(lock: &wb->list_lock);
2075
2076	/*
2077	* Kupdate and background works are special and we want to
2078	* include all inodes that need writing. Livelock avoidance is
2079	* handled by these works yielding to any other work so we are
2080	* safe.
2081	*/
2082	if (work->for_kupdate) {
2083	dirtied_before = jiffies -
2084	msecs_to_jiffies(m: dirty_expire_interval * 10);
2085	} else if (work->for_background)
2086	dirtied_before = jiffies;
2087
2088	trace_writeback_start(wb, work);
2089	if (list_empty(head: &wb->b_io))
2090	queue_io(wb, work, dirtied_before);
2091	if (work->sb)
2092	progress = writeback_sb_inodes(sb: work->sb, wb, work);
2093	else
2094	progress = __writeback_inodes_wb(wb, work);
2095	trace_writeback_written(wb, work);
2096
2097	/*
2098	* Did we write something? Try for more
2099	*
2100	* Dirty inodes are moved to b_io for writeback in batches.
2101	* The completion of the current batch does not necessarily
2102	* mean the overall work is done. So we keep looping as long
2103	* as made some progress on cleaning pages or inodes.
2104	*/
2105	if (progress) {
2106	spin_unlock(lock: &wb->list_lock);
2107	continue;
2108	}
2109
2110	/*
2111	* No more inodes for IO, bail
2112	*/
2113	if (list_empty(head: &wb->b_more_io)) {
2114	spin_unlock(lock: &wb->list_lock);
2115	break;
2116	}
2117
2118	/*
2119	* Nothing written. Wait for some inode to
2120	* become available for writeback. Otherwise
2121	* we'll just busyloop.
2122	*/
2123	trace_writeback_wait(wb, work);
2124	inode = wb_inode(head: wb->b_more_io.prev);
2125	spin_lock(lock: &inode->i_lock);
2126	spin_unlock(lock: &wb->list_lock);
2127	/* This function drops i_lock... */
2128	inode_sleep_on_writeback(inode);
2129	}
2130	blk_finish_plug(&plug);
2131
2132	return nr_pages - work->nr_pages;
2133	}
2134
2135	/*
2136	* Return the next wb_writeback_work struct that hasn't been processed yet.
2137	*/
2138	static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
2139	{
2140	struct wb_writeback_work *work = NULL;
2141
2142	spin_lock_irq(lock: &wb->work_lock);
2143	if (!list_empty(head: &wb->work_list)) {
2144	work = list_entry(wb->work_list.next,
2145	struct wb_writeback_work, list);
2146	list_del_init(entry: &work->list);
2147	}
2148	spin_unlock_irq(lock: &wb->work_lock);
2149	return work;
2150	}
2151
2152	static long wb_check_background_flush(struct bdi_writeback *wb)
2153	{
2154	if (wb_over_bg_thresh(wb)) {
2155
2156	struct wb_writeback_work work = {
2157	.nr_pages = LONG_MAX,
2158	.sync_mode = WB_SYNC_NONE,
2159	.for_background = 1,
2160	.range_cyclic = 1,
2161	.reason = WB_REASON_BACKGROUND,
2162	};
2163
2164	return wb_writeback(wb, work: &work);
2165	}
2166
2167	return 0;
2168	}
2169
2170	static long wb_check_old_data_flush(struct bdi_writeback *wb)
2171	{
2172	unsigned long expired;
2173	long nr_pages;
2174
2175	/*
2176	* When set to zero, disable periodic writeback
2177	*/
2178	if (!dirty_writeback_interval)
2179	return 0;
2180
2181	expired = wb->last_old_flush +
2182	msecs_to_jiffies(m: dirty_writeback_interval * 10);
2183	if (time_before(jiffies, expired))
2184	return 0;
2185
2186	wb->last_old_flush = jiffies;
2187	nr_pages = get_nr_dirty_pages();
2188
2189	if (nr_pages) {
2190	struct wb_writeback_work work = {
2191	.nr_pages = nr_pages,
2192	.sync_mode = WB_SYNC_NONE,
2193	.for_kupdate = 1,
2194	.range_cyclic = 1,
2195	.reason = WB_REASON_PERIODIC,
2196	};
2197
2198	return wb_writeback(wb, work: &work);
2199	}
2200
2201	return 0;
2202	}
2203
2204	static long wb_check_start_all(struct bdi_writeback *wb)
2205	{
2206	long nr_pages;
2207
2208	if (!test_bit(WB_start_all, &wb->state))
2209	return 0;
2210
2211	nr_pages = get_nr_dirty_pages();
2212	if (nr_pages) {
2213	struct wb_writeback_work work = {
2214	.nr_pages = wb_split_bdi_pages(wb, nr_pages),
2215	.sync_mode = WB_SYNC_NONE,
2216	.range_cyclic = 1,
2217	.reason = wb->start_all_reason,
2218	};
2219
2220	nr_pages = wb_writeback(wb, work: &work);
2221	}
2222
2223	clear_bit(nr: WB_start_all, addr: &wb->state);
2224	return nr_pages;
2225	}
2226
2227
2228	/*
2229	* Retrieve work items and do the writeback they describe
2230	*/
2231	static long wb_do_writeback(struct bdi_writeback *wb)
2232	{
2233	struct wb_writeback_work *work;
2234	long wrote = 0;
2235
2236	set_bit(nr: WB_writeback_running, addr: &wb->state);
2237	while ((work = get_next_work_item(wb)) != NULL) {
2238	trace_writeback_exec(wb, work);
2239	wrote += wb_writeback(wb, work);
2240	finish_writeback_work(wb, work);
2241	}
2242
2243	/*
2244	* Check for a flush-everything request
2245	*/
2246	wrote += wb_check_start_all(wb);
2247
2248	/*
2249	* Check for periodic writeback, kupdated() style
2250	*/
2251	wrote += wb_check_old_data_flush(wb);
2252	wrote += wb_check_background_flush(wb);
2253	clear_bit(nr: WB_writeback_running, addr: &wb->state);
2254
2255	return wrote;
2256	}
2257
2258	/*
2259	* Handle writeback of dirty data for the device backed by this bdi. Also
2260	* reschedules periodically and does kupdated style flushing.
2261	*/
2262	void wb_workfn(struct work_struct *work)
2263	{
2264	struct bdi_writeback *wb = container_of(to_delayed_work(work),
2265	struct bdi_writeback, dwork);
2266	long pages_written;
2267
2268	set_worker_desc("flush-%s", bdi_dev_name(bdi: wb->bdi));
2269
2270	if (likely(!current_is_workqueue_rescuer() ||
2271	!test_bit(WB_registered, &wb->state))) {
2272	/*
2273	* The normal path. Keep writing back @wb until its
2274	* work_list is empty. Note that this path is also taken
2275	* if @wb is shutting down even when we're running off the
2276	* rescuer as work_list needs to be drained.
2277	*/
2278	do {
2279	pages_written = wb_do_writeback(wb);
2280	trace_writeback_pages_written(pages_written);
2281	} while (!list_empty(head: &wb->work_list));
2282	} else {
2283	/*
2284	* bdi_wq can't get enough workers and we're running off
2285	* the emergency worker. Don't hog it. Hopefully, 1024 is
2286	* enough for efficient IO.
2287	*/
2288	pages_written = writeback_inodes_wb(wb, nr_pages: 1024,
2289	reason: WB_REASON_FORKER_THREAD);
2290	trace_writeback_pages_written(pages_written);
2291	}
2292
2293	if (!list_empty(head: &wb->work_list))
2294	wb_wakeup(wb);
2295	else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
2296	wb_wakeup_delayed(wb);
2297	}
2298
2299	/*
2300	* Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
2301	* write back the whole world.
2302	*/
2303	static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2304	enum wb_reason reason)
2305	{
2306	struct bdi_writeback *wb;
2307
2308	if (!bdi_has_dirty_io(bdi))
2309	return;
2310
2311	list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2312	wb_start_writeback(wb, reason);
2313	}
2314
2315	void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2316	enum wb_reason reason)
2317	{
2318	rcu_read_lock();
2319	__wakeup_flusher_threads_bdi(bdi, reason);
2320	rcu_read_unlock();
2321	}
2322
2323	/*
2324	* Wakeup the flusher threads to start writeback of all currently dirty pages
2325	*/
2326	void wakeup_flusher_threads(enum wb_reason reason)
2327	{
2328	struct backing_dev_info *bdi;
2329
2330	/*
2331	* If we are expecting writeback progress we must submit plugged IO.
2332	*/
2333	blk_flush_plug(current->plug, async: true);
2334
2335	rcu_read_lock();
2336	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2337	__wakeup_flusher_threads_bdi(bdi, reason);
2338	rcu_read_unlock();
2339	}
2340
2341	/*
2342	* Wake up bdi's periodically to make sure dirtytime inodes gets
2343	* written back periodically. We deliberately do *not* check the
2344	* b_dirtytime list in wb_has_dirty_io(), since this would cause the
2345	* kernel to be constantly waking up once there are any dirtytime
2346	* inodes on the system. So instead we define a separate delayed work
2347	* function which gets called much more rarely. (By default, only
2348	* once every 12 hours.)
2349	*
2350	* If there is any other write activity going on in the file system,
2351	* this function won't be necessary. But if the only thing that has
2352	* happened on the file system is a dirtytime inode caused by an atime
2353	* update, we need this infrastructure below to make sure that inode
2354	* eventually gets pushed out to disk.
2355	*/
2356	static void wakeup_dirtytime_writeback(struct work_struct *w);
2357	static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2358
2359	static void wakeup_dirtytime_writeback(struct work_struct *w)
2360	{
2361	struct backing_dev_info *bdi;
2362
2363	rcu_read_lock();
2364	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
2365	struct bdi_writeback *wb;
2366
2367	list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2368	if (!list_empty(head: &wb->b_dirty_time))
2369	wb_wakeup(wb);
2370	}
2371	rcu_read_unlock();
2372	schedule_delayed_work(dwork: &dirtytime_work, delay: dirtytime_expire_interval * HZ);
2373	}
2374
2375	static int __init start_dirtytime_writeback(void)
2376	{
2377	schedule_delayed_work(dwork: &dirtytime_work, delay: dirtytime_expire_interval * HZ);
2378	return 0;
2379	}
2380	__initcall(start_dirtytime_writeback);
2381
2382	int dirtytime_interval_handler(struct ctl_table *table, int write,
2383	void *buffer, size_t *lenp, loff_t *ppos)
2384	{
2385	int ret;
2386
2387	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2388	if (ret == 0 && write)
2389	mod_delayed_work(wq: system_wq, dwork: &dirtytime_work, delay: 0);
2390	return ret;
2391	}
2392
2393	/**
2394	* __mark_inode_dirty - internal function to mark an inode dirty
2395	*
2396	* @inode: inode to mark
2397	* @flags: what kind of dirty, e.g. I_DIRTY_SYNC. This can be a combination of
2398	* multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
2399	* with I_DIRTY_PAGES.
2400	*
2401	* Mark an inode as dirty. We notify the filesystem, then update the inode's
2402	* dirty flags. Then, if needed we add the inode to the appropriate dirty list.
2403	*
2404	* Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
2405	* instead of calling this directly.
2406	*
2407	* CAREFUL! We only add the inode to the dirty list if it is hashed or if it
2408	* refers to a blockdev. Unhashed inodes will never be added to the dirty list
2409	* even if they are later hashed, as they will have been marked dirty already.
2410	*
2411	* In short, ensure you hash any inodes _before_ you start marking them dirty.
2412	*
2413	* Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2414	* the block-special inode (/dev/hda1) itself. And the ->dirtied_when field of
2415	* the kernel-internal blockdev inode represents the dirtying time of the
2416	* blockdev's pages. This is why for I_DIRTY_PAGES we always use
2417	* page->mapping->host, so the page-dirtying time is recorded in the internal
2418	* blockdev inode.
2419	*/
2420	void __mark_inode_dirty(struct inode *inode, int flags)
2421	{
2422	struct super_block *sb = inode->i_sb;
2423	int dirtytime = 0;
2424	struct bdi_writeback *wb = NULL;
2425
2426	trace_writeback_mark_inode_dirty(inode, flags);
2427
2428	if (flags & I_DIRTY_INODE) {
2429	/*
2430	* Inode timestamp update will piggback on this dirtying.
2431	* We tell ->dirty_inode callback that timestamps need to
2432	* be updated by setting I_DIRTY_TIME in flags.
2433	*/
2434	if (inode->i_state & I_DIRTY_TIME) {
2435	spin_lock(lock: &inode->i_lock);
2436	if (inode->i_state & I_DIRTY_TIME) {
2437	inode->i_state &= ~I_DIRTY_TIME;
2438	flags |= I_DIRTY_TIME;
2439	}
2440	spin_unlock(lock: &inode->i_lock);
2441	}
2442
2443	/*
2444	* Notify the filesystem about the inode being dirtied, so that
2445	* (if needed) it can update on-disk fields and journal the
2446	* inode. This is only needed when the inode itself is being
2447	* dirtied now. I.e. it's only needed for I_DIRTY_INODE, not
2448	* for just I_DIRTY_PAGES or I_DIRTY_TIME.
2449	*/
2450	trace_writeback_dirty_inode_start(inode, flags);
2451	if (sb->s_op->dirty_inode)
2452	sb->s_op->dirty_inode(inode,
2453	flags & (I_DIRTY_INODE | I_DIRTY_TIME));
2454	trace_writeback_dirty_inode(inode, flags);
2455
2456	/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
2457	flags &= ~I_DIRTY_TIME;
2458	} else {
2459	/*
2460	* Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
2461	* (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
2462	* in one call to __mark_inode_dirty().)
2463	*/
2464	dirtytime = flags & I_DIRTY_TIME;
2465	WARN_ON_ONCE(dirtytime && flags != I_DIRTY_TIME);
2466	}
2467
2468	/*
2469	* Paired with smp_mb() in __writeback_single_inode() for the
2470	* following lockless i_state test. See there for details.
2471	*/
2472	smp_mb();
2473
2474	if ((inode->i_state & flags) == flags)
2475	return;
2476
2477	spin_lock(lock: &inode->i_lock);
2478	if ((inode->i_state & flags) != flags) {
2479	const int was_dirty = inode->i_state & I_DIRTY;
2480
2481	inode_attach_wb(inode, NULL);
2482
2483	inode->i_state |= flags;
2484
2485	/*
2486	* Grab inode's wb early because it requires dropping i_lock and we
2487	* need to make sure following checks happen atomically with dirty
2488	* list handling so that we don't move inodes under flush worker's
2489	* hands.
2490	*/
2491	if (!was_dirty) {
2492	wb = locked_inode_to_wb_and_lock_list(inode);
2493	spin_lock(lock: &inode->i_lock);
2494	}
2495
2496	/*
2497	* If the inode is queued for writeback by flush worker, just
2498	* update its dirty state. Once the flush worker is done with
2499	* the inode it will place it on the appropriate superblock
2500	* list, based upon its state.
2501	*/
2502	if (inode->i_state & I_SYNC_QUEUED)
2503	goto out_unlock;
2504
2505	/*
2506	* Only add valid (hashed) inodes to the superblock's
2507	* dirty list. Add blockdev inodes as well.
2508	*/
2509	if (!S_ISBLK(inode->i_mode)) {
2510	if (inode_unhashed(inode))
2511	goto out_unlock;
2512	}
2513	if (inode->i_state & I_FREEING)
2514	goto out_unlock;
2515
2516	/*
2517	* If the inode was already on b_dirty/b_io/b_more_io, don't
2518	* reposition it (that would break b_dirty time-ordering).
2519	*/
2520	if (!was_dirty) {
2521	struct list_head *dirty_list;
2522	bool wakeup_bdi = false;
2523
2524	inode->dirtied_when = jiffies;
2525	if (dirtytime)
2526	inode->dirtied_time_when = jiffies;
2527
2528	if (inode->i_state & I_DIRTY)
2529	dirty_list = &wb->b_dirty;
2530	else
2531	dirty_list = &wb->b_dirty_time;
2532
2533	wakeup_bdi = inode_io_list_move_locked(inode, wb,
2534	head: dirty_list);
2535
2536	spin_unlock(lock: &wb->list_lock);
2537	spin_unlock(lock: &inode->i_lock);
2538	trace_writeback_dirty_inode_enqueue(inode);
2539
2540	/*
2541	* If this is the first dirty inode for this bdi,
2542	* we have to wake-up the corresponding bdi thread
2543	* to make sure background write-back happens
2544	* later.
2545	*/
2546	if (wakeup_bdi &&
2547	(wb->bdi->capabilities & BDI_CAP_WRITEBACK))
2548	wb_wakeup_delayed(wb);
2549	return;
2550	}
2551	}
2552	out_unlock:
2553	if (wb)
2554	spin_unlock(lock: &wb->list_lock);
2555	spin_unlock(lock: &inode->i_lock);
2556	}
2557	EXPORT_SYMBOL(__mark_inode_dirty);
2558
2559	/*
2560	* The @s_sync_lock is used to serialise concurrent sync operations
2561	* to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2562	* Concurrent callers will block on the s_sync_lock rather than doing contending
2563	* walks. The queueing maintains sync(2) required behaviour as all the IO that
2564	* has been issued up to the time this function is enter is guaranteed to be
2565	* completed by the time we have gained the lock and waited for all IO that is
2566	* in progress regardless of the order callers are granted the lock.
2567	*/
2568	static void wait_sb_inodes(struct super_block *sb)
2569	{
2570	LIST_HEAD(sync_list);
2571
2572	/*
2573	* We need to be protected against the filesystem going from
2574	* r/o to r/w or vice versa.
2575	*/
2576	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2577
2578	mutex_lock(&sb->s_sync_lock);
2579
2580	/*
2581	* Splice the writeback list onto a temporary list to avoid waiting on
2582	* inodes that have started writeback after this point.
2583	*
2584	* Use rcu_read_lock() to keep the inodes around until we have a
2585	* reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2586	* the local list because inodes can be dropped from either by writeback
2587	* completion.
2588	*/
2589	rcu_read_lock();
2590	spin_lock_irq(lock: &sb->s_inode_wblist_lock);
2591	list_splice_init(list: &sb->s_inodes_wb, head: &sync_list);
2592
2593	/*
2594	* Data integrity sync. Must wait for all pages under writeback, because
2595	* there may have been pages dirtied before our sync call, but which had
2596	* writeout started before we write it out. In which case, the inode
2597	* may not be on the dirty list, but we still have to wait for that
2598	* writeout.
2599	*/
2600	while (!list_empty(head: &sync_list)) {
2601	struct inode *inode = list_first_entry(&sync_list, struct inode,
2602	i_wb_list);
2603	struct address_space *mapping = inode->i_mapping;
2604
2605	/*
2606	* Move each inode back to the wb list before we drop the lock
2607	* to preserve consistency between i_wb_list and the mapping
2608	* writeback tag. Writeback completion is responsible to remove
2609	* the inode from either list once the writeback tag is cleared.
2610	*/
2611	list_move_tail(list: &inode->i_wb_list, head: &sb->s_inodes_wb);
2612
2613	/*
2614	* The mapping can appear untagged while still on-list since we
2615	* do not have the mapping lock. Skip it here, wb completion
2616	* will remove it.
2617	*/
2618	if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2619	continue;
2620
2621	spin_unlock_irq(lock: &sb->s_inode_wblist_lock);
2622
2623	spin_lock(lock: &inode->i_lock);
2624	if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
2625	spin_unlock(lock: &inode->i_lock);
2626
2627	spin_lock_irq(lock: &sb->s_inode_wblist_lock);
2628	continue;
2629	}
2630	__iget(inode);
2631	spin_unlock(lock: &inode->i_lock);
2632	rcu_read_unlock();
2633
2634	/*
2635	* We keep the error status of individual mapping so that
2636	* applications can catch the writeback error using fsync(2).
2637	* See filemap_fdatawait_keep_errors() for details.
2638	*/
2639	filemap_fdatawait_keep_errors(mapping);
2640
2641	cond_resched();
2642
2643	iput(inode);
2644
2645	rcu_read_lock();
2646	spin_lock_irq(lock: &sb->s_inode_wblist_lock);
2647	}
2648	spin_unlock_irq(lock: &sb->s_inode_wblist_lock);
2649	rcu_read_unlock();
2650	mutex_unlock(lock: &sb->s_sync_lock);
2651	}
2652
2653	static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2654	enum wb_reason reason, bool skip_if_busy)
2655	{
2656	struct backing_dev_info *bdi = sb->s_bdi;
2657	DEFINE_WB_COMPLETION(done, bdi);
2658	struct wb_writeback_work work = {
2659	.sb = sb,
2660	.sync_mode = WB_SYNC_NONE,
2661	.tagged_writepages = 1,
2662	.done = &done,
2663	.nr_pages = nr,
2664	.reason = reason,
2665	};
2666
2667	if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2668	return;
2669	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2670
2671	bdi_split_work_to_wbs(bdi: sb->s_bdi, base_work: &work, skip_if_busy);
2672	wb_wait_for_completion(done: &done);
2673	}
2674
2675	/**
2676	* writeback_inodes_sb_nr - writeback dirty inodes from given super_block
2677	* @sb: the superblock
2678	* @nr: the number of pages to write
2679	* @reason: reason why some writeback work initiated
2680	*
2681	* Start writeback on some inodes on this super_block. No guarantees are made
2682	* on how many (if any) will be written, and this function does not wait
2683	* for IO completion of submitted IO.
2684	*/
2685	void writeback_inodes_sb_nr(struct super_block *sb,
2686	unsigned long nr,
2687	enum wb_reason reason)
2688	{
2689	__writeback_inodes_sb_nr(sb, nr, reason, skip_if_busy: false);
2690	}
2691	EXPORT_SYMBOL(writeback_inodes_sb_nr);
2692
2693	/**
2694	* writeback_inodes_sb - writeback dirty inodes from given super_block
2695	* @sb: the superblock
2696	* @reason: reason why some writeback work was initiated
2697	*
2698	* Start writeback on some inodes on this super_block. No guarantees are made
2699	* on how many (if any) will be written, and this function does not wait
2700	* for IO completion of submitted IO.
2701	*/
2702	void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2703	{
2704	return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2705	}
2706	EXPORT_SYMBOL(writeback_inodes_sb);
2707
2708	/**
2709	* try_to_writeback_inodes_sb - try to start writeback if none underway
2710	* @sb: the superblock
2711	* @reason: reason why some writeback work was initiated
2712	*
2713	* Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2714	*/
2715	void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2716	{
2717	if (!down_read_trylock(sem: &sb->s_umount))
2718	return;
2719
2720	__writeback_inodes_sb_nr(sb, nr: get_nr_dirty_pages(), reason, skip_if_busy: true);
2721	up_read(sem: &sb->s_umount);
2722	}
2723	EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2724
2725	/**
2726	* sync_inodes_sb - sync sb inode pages
2727	* @sb: the superblock
2728	*
2729	* This function writes and waits on any dirty inode belonging to this
2730	* super_block.
2731	*/
2732	void sync_inodes_sb(struct super_block *sb)
2733	{
2734	struct backing_dev_info *bdi = sb->s_bdi;
2735	DEFINE_WB_COMPLETION(done, bdi);
2736	struct wb_writeback_work work = {
2737	.sb = sb,
2738	.sync_mode = WB_SYNC_ALL,
2739	.nr_pages = LONG_MAX,
2740	.range_cyclic = 0,
2741	.done = &done,
2742	.reason = WB_REASON_SYNC,
2743	.for_sync = 1,
2744	};
2745
2746	/*
2747	* Can't skip on !bdi_has_dirty() because we should wait for !dirty
2748	* inodes under writeback and I_DIRTY_TIME inodes ignored by
2749	* bdi_has_dirty() need to be written out too.
2750	*/
2751	if (bdi == &noop_backing_dev_info)
2752	return;
2753	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2754
2755	/* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2756	bdi_down_write_wb_switch_rwsem(bdi);
2757	bdi_split_work_to_wbs(bdi, base_work: &work, skip_if_busy: false);
2758	wb_wait_for_completion(done: &done);
2759	bdi_up_write_wb_switch_rwsem(bdi);
2760
2761	wait_sb_inodes(sb);
2762	}
2763	EXPORT_SYMBOL(sync_inodes_sb);
2764
2765	/**
2766	* write_inode_now - write an inode to disk
2767	* @inode: inode to write to disk
2768	* @sync: whether the write should be synchronous or not
2769	*
2770	* This function commits an inode to disk immediately if it is dirty. This is
2771	* primarily needed by knfsd.
2772	*
2773	* The caller must either have a ref on the inode or must have set I_WILL_FREE.
2774	*/
2775	int write_inode_now(struct inode *inode, int sync)
2776	{
2777	struct writeback_control wbc = {
2778	.nr_to_write = LONG_MAX,
2779	.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2780	.range_start = 0,
2781	.range_end = LLONG_MAX,
2782	};
2783
2784	if (!mapping_can_writeback(mapping: inode->i_mapping))
2785	wbc.nr_to_write = 0;
2786
2787	might_sleep();
2788	return writeback_single_inode(inode, wbc: &wbc);
2789	}
2790	EXPORT_SYMBOL(write_inode_now);
2791
2792	/**
2793	* sync_inode_metadata - write an inode to disk
2794	* @inode: the inode to sync
2795	* @wait: wait for I/O to complete.
2796	*
2797	* Write an inode to disk and adjust its dirty state after completion.
2798	*
2799	* Note: only writes the actual inode, no associated data or other metadata.
2800	*/
2801	int sync_inode_metadata(struct inode *inode, int wait)
2802	{
2803	struct writeback_control wbc = {
2804	.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2805	.nr_to_write = 0, /* metadata-only */
2806	};
2807
2808	return writeback_single_inode(inode, wbc: &wbc);
2809	}
2810	EXPORT_SYMBOL(sync_inode_metadata);
2811