1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2007 Oracle. All rights reserved.
4 * Copyright (C) 2014 Fujitsu. All rights reserved.
5 */
6
7#include <linux/kthread.h>
8#include <linux/slab.h>
9#include <linux/list.h>
10#include <linux/spinlock.h>
11#include <linux/freezer.h>
12#include <trace/events/btrfs.h>
13#include "async-thread.h"
14
15enum {
16 WORK_DONE_BIT,
17 WORK_ORDER_DONE_BIT,
18};
19
20#define NO_THRESHOLD (-1)
21#define DEFAULT_THRESHOLD (32)
22
23struct btrfs_workqueue {
24 struct workqueue_struct *normal_wq;
25
26 /* File system this workqueue services */
27 struct btrfs_fs_info *fs_info;
28
29 /* List head pointing to ordered work list */
30 struct list_head ordered_list;
31
32 /* Spinlock for ordered_list */
33 spinlock_t list_lock;
34
35 /* Thresholding related variants */
36 atomic_t pending;
37
38 /* Up limit of concurrency workers */
39 int limit_active;
40
41 /* Current number of concurrency workers */
42 int current_active;
43
44 /* Threshold to change current_active */
45 int thresh;
46 unsigned int count;
47 spinlock_t thres_lock;
48};
49
50struct btrfs_fs_info * __pure btrfs_workqueue_owner(const struct btrfs_workqueue *wq)
51{
52 return wq->fs_info;
53}
54
55struct btrfs_fs_info * __pure btrfs_work_owner(const struct btrfs_work *work)
56{
57 return work->wq->fs_info;
58}
59
60bool btrfs_workqueue_normal_congested(const struct btrfs_workqueue *wq)
61{
62 /*
63 * We could compare wq->pending with num_online_cpus()
64 * to support "thresh == NO_THRESHOLD" case, but it requires
65 * moving up atomic_inc/dec in thresh_queue/exec_hook. Let's
66 * postpone it until someone needs the support of that case.
67 */
68 if (wq->thresh == NO_THRESHOLD)
69 return false;
70
71 return atomic_read(v: &wq->pending) > wq->thresh * 2;
72}
73
74static void btrfs_init_workqueue(struct btrfs_workqueue *wq,
75 struct btrfs_fs_info *fs_info)
76{
77 wq->fs_info = fs_info;
78 atomic_set(v: &wq->pending, i: 0);
79 INIT_LIST_HEAD(list: &wq->ordered_list);
80 spin_lock_init(&wq->list_lock);
81 spin_lock_init(&wq->thres_lock);
82}
83
84struct btrfs_workqueue *btrfs_alloc_workqueue(struct btrfs_fs_info *fs_info,
85 const char *name, unsigned int flags,
86 int limit_active, int thresh)
87{
88 struct btrfs_workqueue *ret = kzalloc(sizeof(*ret), GFP_KERNEL);
89
90 if (!ret)
91 return NULL;
92
93 btrfs_init_workqueue(wq: ret, fs_info);
94
95 ret->limit_active = limit_active;
96 if (thresh == 0)
97 thresh = DEFAULT_THRESHOLD;
98 /* For low threshold, disabling threshold is a better choice */
99 if (thresh < DEFAULT_THRESHOLD) {
100 ret->current_active = limit_active;
101 ret->thresh = NO_THRESHOLD;
102 } else {
103 /*
104 * For threshold-able wq, let its concurrency grow on demand.
105 * Use minimal max_active at alloc time to reduce resource
106 * usage.
107 */
108 ret->current_active = 1;
109 ret->thresh = thresh;
110 }
111
112 ret->normal_wq = alloc_workqueue("btrfs-%s", flags, ret->current_active,
113 name);
114 if (!ret->normal_wq) {
115 kfree(objp: ret);
116 return NULL;
117 }
118
119 trace_btrfs_workqueue_alloc(wq: ret, name);
120 return ret;
121}
122
123struct btrfs_workqueue *btrfs_alloc_ordered_workqueue(
124 struct btrfs_fs_info *fs_info, const char *name,
125 unsigned int flags)
126{
127 struct btrfs_workqueue *ret;
128
129 ret = kzalloc(sizeof(*ret), GFP_KERNEL);
130 if (!ret)
131 return NULL;
132
133 btrfs_init_workqueue(wq: ret, fs_info);
134
135 /* Ordered workqueues don't allow @max_active adjustments. */
136 ret->limit_active = 1;
137 ret->current_active = 1;
138 ret->thresh = NO_THRESHOLD;
139
140 ret->normal_wq = alloc_ordered_workqueue("btrfs-%s", flags, name);
141 if (!ret->normal_wq) {
142 kfree(objp: ret);
143 return NULL;
144 }
145
146 trace_btrfs_workqueue_alloc(wq: ret, name);
147 return ret;
148}
149
150/*
151 * Hook for threshold which will be called in btrfs_queue_work.
152 * This hook WILL be called in IRQ handler context,
153 * so workqueue_set_max_active MUST NOT be called in this hook
154 */
155static inline void thresh_queue_hook(struct btrfs_workqueue *wq)
156{
157 if (wq->thresh == NO_THRESHOLD)
158 return;
159 atomic_inc(v: &wq->pending);
160}
161
162/*
163 * Hook for threshold which will be called before executing the work,
164 * This hook is called in kthread content.
165 * So workqueue_set_max_active is called here.
166 */
167static inline void thresh_exec_hook(struct btrfs_workqueue *wq)
168{
169 int new_current_active;
170 long pending;
171 bool need_change = false;
172
173 if (wq->thresh == NO_THRESHOLD)
174 return;
175
176 atomic_dec(v: &wq->pending);
177 spin_lock(lock: &wq->thres_lock);
178 /*
179 * Use wq->count to limit the calling frequency of
180 * workqueue_set_max_active.
181 */
182 wq->count++;
183 wq->count %= (wq->thresh / 4);
184 if (!wq->count)
185 goto out;
186 new_current_active = wq->current_active;
187
188 /*
189 * pending may be changed later, but it's OK since we really
190 * don't need it so accurate to calculate new_max_active.
191 */
192 pending = atomic_read(v: &wq->pending);
193 if (pending > wq->thresh)
194 new_current_active++;
195 if (pending < wq->thresh / 2)
196 new_current_active--;
197 new_current_active = clamp_val(new_current_active, 1, wq->limit_active);
198 if (new_current_active != wq->current_active) {
199 need_change = true;
200 wq->current_active = new_current_active;
201 }
202out:
203 spin_unlock(lock: &wq->thres_lock);
204
205 if (need_change)
206 workqueue_set_max_active(wq: wq->normal_wq, max_active: wq->current_active);
207}
208
209static void run_ordered_work(struct btrfs_workqueue *wq,
210 struct btrfs_work *self)
211{
212 struct list_head *list = &wq->ordered_list;
213 struct btrfs_work *work;
214 spinlock_t *lock = &wq->list_lock;
215 unsigned long flags;
216 bool free_self = false;
217
218 while (1) {
219 spin_lock_irqsave(lock, flags);
220 if (list_empty(head: list))
221 break;
222 work = list_first_entry(list, struct btrfs_work, ordered_list);
223 if (!test_bit(WORK_DONE_BIT, &work->flags))
224 break;
225 /*
226 * Orders all subsequent loads after reading WORK_DONE_BIT,
227 * paired with the smp_mb__before_atomic in btrfs_work_helper
228 * this guarantees that the ordered function will see all
229 * updates from ordinary work function.
230 */
231 smp_rmb();
232
233 /*
234 * we are going to call the ordered done function, but
235 * we leave the work item on the list as a barrier so
236 * that later work items that are done don't have their
237 * functions called before this one returns
238 */
239 if (test_and_set_bit(nr: WORK_ORDER_DONE_BIT, addr: &work->flags))
240 break;
241 trace_btrfs_ordered_sched(work);
242 spin_unlock_irqrestore(lock, flags);
243 work->ordered_func(work, false);
244
245 /* now take the lock again and drop our item from the list */
246 spin_lock_irqsave(lock, flags);
247 list_del(entry: &work->ordered_list);
248 spin_unlock_irqrestore(lock, flags);
249
250 if (work == self) {
251 /*
252 * This is the work item that the worker is currently
253 * executing.
254 *
255 * The kernel workqueue code guarantees non-reentrancy
256 * of work items. I.e., if a work item with the same
257 * address and work function is queued twice, the second
258 * execution is blocked until the first one finishes. A
259 * work item may be freed and recycled with the same
260 * work function; the workqueue code assumes that the
261 * original work item cannot depend on the recycled work
262 * item in that case (see find_worker_executing_work()).
263 *
264 * Note that different types of Btrfs work can depend on
265 * each other, and one type of work on one Btrfs
266 * filesystem may even depend on the same type of work
267 * on another Btrfs filesystem via, e.g., a loop device.
268 * Therefore, we must not allow the current work item to
269 * be recycled until we are really done, otherwise we
270 * break the above assumption and can deadlock.
271 */
272 free_self = true;
273 } else {
274 /*
275 * We don't want to call the ordered free functions with
276 * the lock held.
277 */
278 work->ordered_func(work, true);
279 /* NB: work must not be dereferenced past this point. */
280 trace_btrfs_all_work_done(fs_info: wq->fs_info, wtag: work);
281 }
282 }
283 spin_unlock_irqrestore(lock, flags);
284
285 if (free_self) {
286 self->ordered_func(self, true);
287 /* NB: self must not be dereferenced past this point. */
288 trace_btrfs_all_work_done(fs_info: wq->fs_info, wtag: self);
289 }
290}
291
292static void btrfs_work_helper(struct work_struct *normal_work)
293{
294 struct btrfs_work *work = container_of(normal_work, struct btrfs_work,
295 normal_work);
296 struct btrfs_workqueue *wq = work->wq;
297 bool need_order = false;
298
299 /*
300 * We should not touch things inside work in the following cases:
301 * 1) after work->func() if it has no ordered_func(..., true) to free
302 * Since the struct is freed in work->func().
303 * 2) after setting WORK_DONE_BIT
304 * The work may be freed in other threads almost instantly.
305 * So we save the needed things here.
306 */
307 if (work->ordered_func)
308 need_order = true;
309
310 trace_btrfs_work_sched(work);
311 thresh_exec_hook(wq);
312 work->func(work);
313 if (need_order) {
314 /*
315 * Ensures all memory accesses done in the work function are
316 * ordered before setting the WORK_DONE_BIT. Ensuring the thread
317 * which is going to executed the ordered work sees them.
318 * Pairs with the smp_rmb in run_ordered_work.
319 */
320 smp_mb__before_atomic();
321 set_bit(nr: WORK_DONE_BIT, addr: &work->flags);
322 run_ordered_work(wq, self: work);
323 } else {
324 /* NB: work must not be dereferenced past this point. */
325 trace_btrfs_all_work_done(fs_info: wq->fs_info, wtag: work);
326 }
327}
328
329void btrfs_init_work(struct btrfs_work *work, btrfs_func_t func,
330 btrfs_ordered_func_t ordered_func)
331{
332 work->func = func;
333 work->ordered_func = ordered_func;
334 INIT_WORK(&work->normal_work, btrfs_work_helper);
335 INIT_LIST_HEAD(list: &work->ordered_list);
336 work->flags = 0;
337}
338
339void btrfs_queue_work(struct btrfs_workqueue *wq, struct btrfs_work *work)
340{
341 unsigned long flags;
342
343 work->wq = wq;
344 thresh_queue_hook(wq);
345 if (work->ordered_func) {
346 spin_lock_irqsave(&wq->list_lock, flags);
347 list_add_tail(new: &work->ordered_list, head: &wq->ordered_list);
348 spin_unlock_irqrestore(lock: &wq->list_lock, flags);
349 }
350 trace_btrfs_work_queued(work);
351 queue_work(wq: wq->normal_wq, work: &work->normal_work);
352}
353
354void btrfs_destroy_workqueue(struct btrfs_workqueue *wq)
355{
356 if (!wq)
357 return;
358 destroy_workqueue(wq: wq->normal_wq);
359 trace_btrfs_workqueue_destroy(wq);
360 kfree(objp: wq);
361}
362
363void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int limit_active)
364{
365 if (wq)
366 wq->limit_active = limit_active;
367}
368
369void btrfs_flush_workqueue(struct btrfs_workqueue *wq)
370{
371 flush_workqueue(wq->normal_wq);
372}
373

source code of linux/fs/btrfs/async-thread.c