1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Copyright (C) 2019-2023 Oracle. All Rights Reserved.
4 * Author: Darrick J. Wong <djwong@kernel.org>
5 */
6#include "xfs.h"
7#include "xfs_fs.h"
8#include "xfs_shared.h"
9#include "xfs_format.h"
10#include "xfs_trans_resv.h"
11#include "xfs_log_format.h"
12#include "xfs_trans.h"
13#include "xfs_mount.h"
14#include "xfs_alloc.h"
15#include "xfs_ialloc.h"
16#include "xfs_health.h"
17#include "xfs_btree.h"
18#include "xfs_ag.h"
19#include "xfs_rtbitmap.h"
20#include "xfs_inode.h"
21#include "xfs_icache.h"
22#include "xfs_rtgroup.h"
23#include "scrub/scrub.h"
24#include "scrub/common.h"
25#include "scrub/trace.h"
26#include "scrub/fscounters.h"
27
28/*
29 * FS Summary Counters
30 * ===================
31 *
32 * The basics of filesystem summary counter checking are that we iterate the
33 * AGs counting the number of free blocks, free space btree blocks, per-AG
34 * reservations, inodes, delayed allocation reservations, and free inodes.
35 * Then we compare what we computed against the in-core counters.
36 *
37 * However, the reality is that summary counters are a tricky beast to check.
38 * While we /could/ freeze the filesystem and scramble around the AGs counting
39 * the free blocks, in practice we prefer not do that for a scan because
40 * freezing is costly. To get around this, we added a per-cpu counter of the
41 * delalloc reservations so that we can rotor around the AGs relatively
42 * quickly, and we allow the counts to be slightly off because we're not taking
43 * any locks while we do this.
44 *
45 * So the first thing we do is warm up the buffer cache in the setup routine by
46 * walking all the AGs to make sure the incore per-AG structure has been
47 * initialized. The expected value calculation then iterates the incore per-AG
48 * structures as quickly as it can. We snapshot the percpu counters before and
49 * after this operation and use the difference in counter values to guess at
50 * our tolerance for mismatch between expected and actual counter values.
51 */
52
53/*
54 * Since the expected value computation is lockless but only browses incore
55 * values, the percpu counters should be fairly close to each other. However,
56 * we'll allow ourselves to be off by at least this (arbitrary) amount.
57 */
58#define XCHK_FSCOUNT_MIN_VARIANCE (512)
59
60/*
61 * Make sure the per-AG structure has been initialized from the on-disk header
62 * contents and trust that the incore counters match the ondisk counters. (The
63 * AGF and AGI scrubbers check them, and a normal xfs_scrub run checks the
64 * summary counters after checking all AG headers). Do this from the setup
65 * function so that the inner AG aggregation loop runs as quickly as possible.
66 *
67 * This function runs during the setup phase /before/ we start checking any
68 * metadata.
69 */
70STATIC int
71xchk_fscount_warmup(
72 struct xfs_scrub *sc)
73{
74 struct xfs_mount *mp = sc->mp;
75 struct xfs_buf *agi_bp = NULL;
76 struct xfs_buf *agf_bp = NULL;
77 struct xfs_perag *pag = NULL;
78 int error = 0;
79
80 while ((pag = xfs_perag_next(mp, pag))) {
81 if (xchk_should_terminate(sc, &error))
82 break;
83 if (xfs_perag_initialised_agi(pag) &&
84 xfs_perag_initialised_agf(pag))
85 continue;
86
87 /* Lock both AG headers. */
88 error = xfs_ialloc_read_agi(pag, sc->tp, 0, &agi_bp);
89 if (error)
90 break;
91 error = xfs_alloc_read_agf(pag, sc->tp, 0, &agf_bp);
92 if (error)
93 break;
94
95 /*
96 * These are supposed to be initialized by the header read
97 * function.
98 */
99 if (!xfs_perag_initialised_agi(pag) ||
100 !xfs_perag_initialised_agf(pag)) {
101 error = -EFSCORRUPTED;
102 break;
103 }
104
105 xfs_buf_relse(agf_bp);
106 agf_bp = NULL;
107 xfs_buf_relse(agi_bp);
108 agi_bp = NULL;
109 }
110
111 if (agf_bp)
112 xfs_buf_relse(agf_bp);
113 if (agi_bp)
114 xfs_buf_relse(agi_bp);
115 if (pag)
116 xfs_perag_rele(pag);
117 return error;
118}
119
120static inline int
121xchk_fsfreeze(
122 struct xfs_scrub *sc)
123{
124 int error;
125
126 error = freeze_super(sc->mp->m_super, FREEZE_HOLDER_KERNEL, NULL);
127 trace_xchk_fsfreeze(sc, error);
128 return error;
129}
130
131static inline int
132xchk_fsthaw(
133 struct xfs_scrub *sc)
134{
135 int error;
136
137 /* This should always succeed, we have a kernel freeze */
138 error = thaw_super(sc->mp->m_super, FREEZE_HOLDER_KERNEL, NULL);
139 trace_xchk_fsthaw(sc, error);
140 return error;
141}
142
143/*
144 * We couldn't stabilize the filesystem long enough to sample all the variables
145 * that comprise the summary counters and compare them to the percpu counters.
146 * We need to disable all writer threads, which means taking the first two
147 * freeze levels to put userspace to sleep, and the third freeze level to
148 * prevent background threads from starting new transactions. Take one level
149 * more to prevent other callers from unfreezing the filesystem while we run.
150 */
151STATIC int
152xchk_fscounters_freeze(
153 struct xfs_scrub *sc)
154{
155 struct xchk_fscounters *fsc = sc->buf;
156 int error = 0;
157
158 if (sc->flags & XCHK_HAVE_FREEZE_PROT) {
159 sc->flags &= ~XCHK_HAVE_FREEZE_PROT;
160 mnt_drop_write_file(sc->file);
161 }
162
163 /* Try to grab a kernel freeze. */
164 while ((error = xchk_fsfreeze(sc)) == -EBUSY) {
165 if (xchk_should_terminate(sc, &error))
166 return error;
167
168 delay(HZ / 10);
169 }
170 if (error)
171 return error;
172
173 fsc->frozen = true;
174 return 0;
175}
176
177/* Thaw the filesystem after checking or repairing fscounters. */
178STATIC void
179xchk_fscounters_cleanup(
180 void *buf)
181{
182 struct xchk_fscounters *fsc = buf;
183 struct xfs_scrub *sc = fsc->sc;
184 int error;
185
186 if (!fsc->frozen)
187 return;
188
189 error = xchk_fsthaw(sc);
190 if (error)
191 xfs_emerg(sc->mp, "still frozen after scrub, err=%d", error);
192 else
193 fsc->frozen = false;
194}
195
196int
197xchk_setup_fscounters(
198 struct xfs_scrub *sc)
199{
200 struct xchk_fscounters *fsc;
201 int error;
202
203 /*
204 * If the AGF doesn't track btreeblks, we have to lock the AGF to count
205 * btree block usage by walking the actual btrees.
206 */
207 if (!xfs_has_lazysbcount(sc->mp))
208 xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
209
210 sc->buf = kzalloc(sizeof(struct xchk_fscounters), XCHK_GFP_FLAGS);
211 if (!sc->buf)
212 return -ENOMEM;
213 sc->buf_cleanup = xchk_fscounters_cleanup;
214 fsc = sc->buf;
215 fsc->sc = sc;
216
217 xfs_icount_range(sc->mp, &fsc->icount_min, &fsc->icount_max);
218
219 /* We must get the incore counters set up before we can proceed. */
220 error = xchk_fscount_warmup(sc);
221 if (error)
222 return error;
223
224 /*
225 * Pause all writer activity in the filesystem while we're scrubbing to
226 * reduce the likelihood of background perturbations to the counters
227 * throwing off our calculations.
228 *
229 * If we're repairing, we need to prevent any other thread from
230 * changing the global fs summary counters while we're repairing them.
231 * This requires the fs to be frozen, which will disable background
232 * reclaim and purge all inactive inodes.
233 */
234 if ((sc->flags & XCHK_TRY_HARDER) || xchk_could_repair(sc)) {
235 error = xchk_fscounters_freeze(sc);
236 if (error)
237 return error;
238 }
239
240 xchk_trans_alloc_empty(sc);
241 return 0;
242}
243
244/*
245 * Part 1: Collecting filesystem summary counts. For each AG, we add its
246 * summary counts (total inodes, free inodes, free data blocks) to an incore
247 * copy of the overall filesystem summary counts.
248 *
249 * To avoid false corruption reports in part 2, any failure in this part must
250 * set the INCOMPLETE flag even when a negative errno is returned. This care
251 * must be taken with certain errno values (i.e. EFSBADCRC, EFSCORRUPTED,
252 * ECANCELED) that are absorbed into a scrub state flag update by
253 * xchk_*_process_error. Scrub and repair share the same incore data
254 * structures, so the INCOMPLETE flag is critical to prevent a repair based on
255 * insufficient information.
256 */
257
258/* Count free space btree blocks manually for pre-lazysbcount filesystems. */
259static int
260xchk_fscount_btreeblks(
261 struct xfs_scrub *sc,
262 struct xchk_fscounters *fsc,
263 xfs_agnumber_t agno)
264{
265 xfs_filblks_t blocks;
266 int error;
267
268 error = xchk_ag_init_existing(sc, agno, &sc->sa);
269 if (error)
270 goto out_free;
271
272 error = xfs_btree_count_blocks(sc->sa.bno_cur, &blocks);
273 if (error)
274 goto out_free;
275 fsc->fdblocks += blocks - 1;
276
277 error = xfs_btree_count_blocks(sc->sa.cnt_cur, &blocks);
278 if (error)
279 goto out_free;
280 fsc->fdblocks += blocks - 1;
281
282out_free:
283 xchk_ag_free(sc, &sc->sa);
284 return error;
285}
286
287/*
288 * Calculate what the global in-core counters ought to be from the incore
289 * per-AG structure. Callers can compare this to the actual in-core counters
290 * to estimate by how much both in-core and on-disk counters need to be
291 * adjusted.
292 */
293STATIC int
294xchk_fscount_aggregate_agcounts(
295 struct xfs_scrub *sc,
296 struct xchk_fscounters *fsc)
297{
298 struct xfs_mount *mp = sc->mp;
299 struct xfs_perag *pag = NULL;
300 uint64_t delayed;
301 int tries = 8;
302 int error = 0;
303
304retry:
305 fsc->icount = 0;
306 fsc->ifree = 0;
307 fsc->fdblocks = 0;
308
309 while ((pag = xfs_perag_next(mp, pag))) {
310 if (xchk_should_terminate(sc, &error))
311 break;
312
313 /* This somehow got unset since the warmup? */
314 if (!xfs_perag_initialised_agi(pag) ||
315 !xfs_perag_initialised_agf(pag)) {
316 error = -EFSCORRUPTED;
317 break;
318 }
319
320 /* Count all the inodes */
321 fsc->icount += pag->pagi_count;
322 fsc->ifree += pag->pagi_freecount;
323
324 /* Add up the free/freelist/bnobt/cntbt blocks */
325 fsc->fdblocks += pag->pagf_freeblks;
326 fsc->fdblocks += pag->pagf_flcount;
327 if (xfs_has_lazysbcount(sc->mp)) {
328 fsc->fdblocks += pag->pagf_btreeblks;
329 } else {
330 error = xchk_fscount_btreeblks(sc, fsc, pag_agno(pag));
331 if (error)
332 break;
333 }
334
335 /*
336 * Per-AG reservations are taken out of the incore counters,
337 * so they must be left out of the free blocks computation.
338 */
339 fsc->fdblocks -= pag->pag_meta_resv.ar_reserved;
340 fsc->fdblocks -= pag->pag_rmapbt_resv.ar_orig_reserved;
341
342 }
343 if (pag)
344 xfs_perag_rele(pag);
345 if (error) {
346 xchk_set_incomplete(sc);
347 return error;
348 }
349
350 /*
351 * The global incore space reservation is taken from the incore
352 * counters, so leave that out of the computation.
353 */
354 fsc->fdblocks -= mp->m_free[XC_FREE_BLOCKS].res_avail;
355
356 /*
357 * Delayed allocation reservations are taken out of the incore counters
358 * but not recorded on disk, so leave them and their indlen blocks out
359 * of the computation.
360 */
361 delayed = percpu_counter_sum(&mp->m_delalloc_blks);
362 fsc->fdblocks -= delayed;
363
364 trace_xchk_fscounters_calc(mp, fsc->icount, fsc->ifree, fsc->fdblocks,
365 delayed);
366
367
368 /* Bail out if the values we compute are totally nonsense. */
369 if (fsc->icount < fsc->icount_min || fsc->icount > fsc->icount_max ||
370 fsc->fdblocks > mp->m_sb.sb_dblocks ||
371 fsc->ifree > fsc->icount_max)
372 return -EFSCORRUPTED;
373
374 /*
375 * If ifree > icount then we probably had some perturbation in the
376 * counters while we were calculating things. We'll try a few times
377 * to maintain ifree <= icount before giving up.
378 */
379 if (fsc->ifree > fsc->icount) {
380 if (tries--)
381 goto retry;
382 return -EDEADLOCK;
383 }
384
385 return 0;
386}
387
388#ifdef CONFIG_XFS_RT
389STATIC int
390xchk_fscount_add_frextent(
391 struct xfs_rtgroup *rtg,
392 struct xfs_trans *tp,
393 const struct xfs_rtalloc_rec *rec,
394 void *priv)
395{
396 struct xchk_fscounters *fsc = priv;
397 int error = 0;
398
399 fsc->frextents += rec->ar_extcount;
400
401 xchk_should_terminate(fsc->sc, &error);
402 return error;
403}
404
405/* Calculate the number of free realtime extents from the realtime bitmap. */
406STATIC int
407xchk_fscount_count_frextents(
408 struct xfs_scrub *sc,
409 struct xchk_fscounters *fsc)
410{
411 struct xfs_mount *mp = sc->mp;
412 struct xfs_rtgroup *rtg = NULL;
413 int error;
414
415 fsc->frextents = 0;
416 fsc->frextents_delayed = 0;
417
418 /*
419 * Don't bother verifying and repairing the fs counters for zoned file
420 * systems as they don't track an on-disk frextents count, and the
421 * in-memory percpu counter also includes reservations.
422 */
423 if (!xfs_has_realtime(mp) || xfs_has_zoned(mp))
424 return 0;
425
426 while ((rtg = xfs_rtgroup_next(mp, rtg))) {
427 xfs_rtgroup_lock(rtg, XFS_RTGLOCK_BITMAP_SHARED);
428 error = xfs_rtalloc_query_all(rtg, sc->tp,
429 xchk_fscount_add_frextent, fsc);
430 xfs_rtgroup_unlock(rtg, XFS_RTGLOCK_BITMAP_SHARED);
431 if (error) {
432 xchk_set_incomplete(sc);
433 xfs_rtgroup_rele(rtg);
434 return error;
435 }
436 }
437
438 fsc->frextents_delayed = percpu_counter_sum(&mp->m_delalloc_rtextents);
439 return 0;
440}
441#else
442STATIC int
443xchk_fscount_count_frextents(
444 struct xfs_scrub *sc,
445 struct xchk_fscounters *fsc)
446{
447 fsc->frextents = 0;
448 fsc->frextents_delayed = 0;
449 return 0;
450}
451#endif /* CONFIG_XFS_RT */
452
453/*
454 * Part 2: Comparing filesystem summary counters. All we have to do here is
455 * sum the percpu counters and compare them to what we've observed.
456 */
457
458/*
459 * Is the @counter reasonably close to the @expected value?
460 *
461 * We neither locked nor froze anything in the filesystem while aggregating the
462 * per-AG data to compute the @expected value, which means that the counter
463 * could have changed. We know the @old_value of the summation of the counter
464 * before the aggregation, and we re-sum the counter now. If the expected
465 * value falls between the two summations, we're ok.
466 *
467 * Otherwise, we /might/ have a problem. If the change in the summations is
468 * more than we want to tolerate, the filesystem is probably busy and we should
469 * just send back INCOMPLETE and see if userspace will try again.
470 *
471 * If we're repairing then we require an exact match.
472 */
473static inline bool
474xchk_fscount_within_range(
475 struct xfs_scrub *sc,
476 const int64_t old_value,
477 struct percpu_counter *counter,
478 uint64_t expected)
479{
480 int64_t min_value, max_value;
481 int64_t curr_value = percpu_counter_sum(counter);
482
483 trace_xchk_fscounters_within_range(sc->mp, expected, curr_value,
484 old_value);
485
486 /* Negative values are always wrong. */
487 if (curr_value < 0)
488 return false;
489
490 /* Exact matches are always ok. */
491 if (curr_value == expected)
492 return true;
493
494 /* We require exact matches when repair is running. */
495 if (sc->sm->sm_flags & XFS_SCRUB_IFLAG_REPAIR)
496 return false;
497
498 min_value = min(old_value, curr_value);
499 max_value = max(old_value, curr_value);
500
501 /* Within the before-and-after range is ok. */
502 if (expected >= min_value && expected <= max_value)
503 return true;
504
505 /* Everything else is bad. */
506 return false;
507}
508
509/* Check the superblock counters. */
510int
511xchk_fscounters(
512 struct xfs_scrub *sc)
513{
514 struct xfs_mount *mp = sc->mp;
515 struct xchk_fscounters *fsc = sc->buf;
516 int64_t icount, ifree, fdblocks, frextents;
517 bool try_again = false;
518 int error;
519
520 /* Snapshot the percpu counters. */
521 icount = percpu_counter_sum(&mp->m_icount);
522 ifree = percpu_counter_sum(&mp->m_ifree);
523 fdblocks = xfs_sum_freecounter_raw(mp, XC_FREE_BLOCKS);
524 frextents = xfs_sum_freecounter_raw(mp, XC_FREE_RTEXTENTS);
525
526 /* No negative values, please! */
527 if (icount < 0 || ifree < 0)
528 xchk_set_corrupt(sc);
529
530 /*
531 * If the filesystem is not frozen, the counter summation calls above
532 * can race with xfs_dec_freecounter, which subtracts a requested space
533 * reservation from the counter and undoes the subtraction if that made
534 * the counter go negative. Therefore, it's possible to see negative
535 * values here, and we should only flag that as a corruption if we
536 * froze the fs. This is much more likely to happen with frextents
537 * since there are no reserved pools.
538 */
539 if (fdblocks < 0 || frextents < 0) {
540 if (!fsc->frozen)
541 return -EDEADLOCK;
542
543 xchk_set_corrupt(sc);
544 return 0;
545 }
546
547 /* See if icount is obviously wrong. */
548 if (icount < fsc->icount_min || icount > fsc->icount_max)
549 xchk_set_corrupt(sc);
550
551 /* See if fdblocks is obviously wrong. */
552 if (fdblocks > mp->m_sb.sb_dblocks)
553 xchk_set_corrupt(sc);
554
555 /* See if frextents is obviously wrong. */
556 if (frextents > mp->m_sb.sb_rextents)
557 xchk_set_corrupt(sc);
558
559 /*
560 * If ifree exceeds icount by more than the minimum variance then
561 * something's probably wrong with the counters.
562 */
563 if (ifree > icount && ifree - icount > XCHK_FSCOUNT_MIN_VARIANCE)
564 xchk_set_corrupt(sc);
565
566 /* Walk the incore AG headers to calculate the expected counters. */
567 error = xchk_fscount_aggregate_agcounts(sc, fsc);
568 if (!xchk_process_error(sc, 0, XFS_SB_BLOCK(mp), &error))
569 return error;
570
571 /* Count the free extents counter for rt volumes. */
572 error = xchk_fscount_count_frextents(sc, fsc);
573 if (!xchk_process_error(sc, 0, XFS_SB_BLOCK(mp), &error))
574 return error;
575 if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_INCOMPLETE)
576 return 0;
577
578 /*
579 * Compare the in-core counters with whatever we counted. If the fs is
580 * frozen, we treat the discrepancy as a corruption because the freeze
581 * should have stabilized the counter values. Otherwise, we need
582 * userspace to call us back having granted us freeze permission.
583 */
584 if (!xchk_fscount_within_range(sc, icount, &mp->m_icount,
585 fsc->icount)) {
586 if (fsc->frozen)
587 xchk_set_corrupt(sc);
588 else
589 try_again = true;
590 }
591
592 if (!xchk_fscount_within_range(sc, ifree, &mp->m_ifree, fsc->ifree)) {
593 if (fsc->frozen)
594 xchk_set_corrupt(sc);
595 else
596 try_again = true;
597 }
598
599 if (!xchk_fscount_within_range(sc, fdblocks,
600 &mp->m_free[XC_FREE_BLOCKS].count, fsc->fdblocks)) {
601 if (fsc->frozen)
602 xchk_set_corrupt(sc);
603 else
604 try_again = true;
605 }
606
607 if (!xfs_has_zoned(mp) &&
608 !xchk_fscount_within_range(sc, frextents,
609 &mp->m_free[XC_FREE_RTEXTENTS].count,
610 fsc->frextents - fsc->frextents_delayed)) {
611 if (fsc->frozen)
612 xchk_set_corrupt(sc);
613 else
614 try_again = true;
615 }
616
617 if (try_again)
618 return -EDEADLOCK;
619
620 return 0;
621}
622

source code of linux/fs/xfs/scrub/fscounters.c