summaryrefslogtreecommitdiff
path: root/fs/xfs/scrub/fscounters.c
blob: ec2064ed3c30f4549de65a5726f8b14f1f177fd6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (C) 2019 Oracle.  All Rights Reserved.
 * Author: Darrick J. Wong <darrick.wong@oracle.com>
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_sb.h"
#include "xfs_alloc.h"
#include "xfs_ialloc.h"
#include "xfs_health.h"
#include "scrub/scrub.h"
#include "scrub/common.h"
#include "scrub/trace.h"

/*
 * FS Summary Counters
 * ===================
 *
 * The basics of filesystem summary counter checking are that we iterate the
 * AGs counting the number of free blocks, free space btree blocks, per-AG
 * reservations, inodes, delayed allocation reservations, and free inodes.
 * Then we compare what we computed against the in-core counters.
 *
 * However, the reality is that summary counters are a tricky beast to check.
 * While we /could/ freeze the filesystem and scramble around the AGs counting
 * the free blocks, in practice we prefer not do that for a scan because
 * freezing is costly.  To get around this, we added a per-cpu counter of the
 * delalloc reservations so that we can rotor around the AGs relatively
 * quickly, and we allow the counts to be slightly off because we're not taking
 * any locks while we do this.
 *
 * So the first thing we do is warm up the buffer cache in the setup routine by
 * walking all the AGs to make sure the incore per-AG structure has been
 * initialized.  The expected value calculation then iterates the incore per-AG
 * structures as quickly as it can.  We snapshot the percpu counters before and
 * after this operation and use the difference in counter values to guess at
 * our tolerance for mismatch between expected and actual counter values.
 */

/*
 * Since the expected value computation is lockless but only browses incore
 * values, the percpu counters should be fairly close to each other.  However,
 * we'll allow ourselves to be off by at least this (arbitrary) amount.
 */
#define XCHK_FSCOUNT_MIN_VARIANCE	(512)

/*
 * Make sure the per-AG structure has been initialized from the on-disk header
 * contents and trust that the incore counters match the ondisk counters.  (The
 * AGF and AGI scrubbers check them, and a normal xfs_scrub run checks the
 * summary counters after checking all AG headers).  Do this from the setup
 * function so that the inner AG aggregation loop runs as quickly as possible.
 *
 * This function runs during the setup phase /before/ we start checking any
 * metadata.
 */
STATIC int
xchk_fscount_warmup(
	struct xfs_scrub	*sc)
{
	struct xfs_mount	*mp = sc->mp;
	struct xfs_buf		*agi_bp = NULL;
	struct xfs_buf		*agf_bp = NULL;
	struct xfs_perag	*pag = NULL;
	xfs_agnumber_t		agno;
	int			error = 0;

	for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
		pag = xfs_perag_get(mp, agno);

		if (pag->pagi_init && pag->pagf_init)
			goto next_loop_perag;

		/* Lock both AG headers. */
		error = xfs_ialloc_read_agi(mp, sc->tp, agno, &agi_bp);
		if (error)
			break;
		error = xfs_alloc_read_agf(mp, sc->tp, agno, 0, &agf_bp);
		if (error)
			break;

		/*
		 * These are supposed to be initialized by the header read
		 * function.
		 */
		error = -EFSCORRUPTED;
		if (!pag->pagi_init || !pag->pagf_init)
			break;

		xfs_buf_relse(agf_bp);
		agf_bp = NULL;
		xfs_buf_relse(agi_bp);
		agi_bp = NULL;
next_loop_perag:
		xfs_perag_put(pag);
		pag = NULL;
		error = 0;

		if (xchk_should_terminate(sc, &error))
			break;
	}

	if (agf_bp)
		xfs_buf_relse(agf_bp);
	if (agi_bp)
		xfs_buf_relse(agi_bp);
	if (pag)
		xfs_perag_put(pag);
	return error;
}

int
xchk_setup_fscounters(
	struct xfs_scrub	*sc,
	struct xfs_inode	*ip)
{
	struct xchk_fscounters	*fsc;
	int			error;

	sc->buf = kmem_zalloc(sizeof(struct xchk_fscounters), 0);
	if (!sc->buf)
		return -ENOMEM;
	fsc = sc->buf;

	xfs_icount_range(sc->mp, &fsc->icount_min, &fsc->icount_max);

	/* We must get the incore counters set up before we can proceed. */
	error = xchk_fscount_warmup(sc);
	if (error)
		return error;

	/*
	 * Pause background reclaim while we're scrubbing to reduce the
	 * likelihood of background perturbations to the counters throwing off
	 * our calculations.
	 */
	xchk_stop_reaping(sc);

	return xchk_trans_alloc(sc, 0);
}

/*
 * Calculate what the global in-core counters ought to be from the incore
 * per-AG structure.  Callers can compare this to the actual in-core counters
 * to estimate by how much both in-core and on-disk counters need to be
 * adjusted.
 */
STATIC int
xchk_fscount_aggregate_agcounts(
	struct xfs_scrub	*sc,
	struct xchk_fscounters	*fsc)
{
	struct xfs_mount	*mp = sc->mp;
	struct xfs_perag	*pag;
	uint64_t		delayed;
	xfs_agnumber_t		agno;
	int			tries = 8;
	int			error = 0;

retry:
	fsc->icount = 0;
	fsc->ifree = 0;
	fsc->fdblocks = 0;

	for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
		pag = xfs_perag_get(mp, agno);

		/* This somehow got unset since the warmup? */
		if (!pag->pagi_init || !pag->pagf_init) {
			xfs_perag_put(pag);
			return -EFSCORRUPTED;
		}

		/* Count all the inodes */
		fsc->icount += pag->pagi_count;
		fsc->ifree += pag->pagi_freecount;

		/* Add up the free/freelist/bnobt/cntbt blocks */
		fsc->fdblocks += pag->pagf_freeblks;
		fsc->fdblocks += pag->pagf_flcount;
		fsc->fdblocks += pag->pagf_btreeblks;

		/*
		 * Per-AG reservations are taken out of the incore counters,
		 * so they must be left out of the free blocks computation.
		 */
		fsc->fdblocks -= pag->pag_meta_resv.ar_reserved;
		fsc->fdblocks -= pag->pag_rmapbt_resv.ar_orig_reserved;

		xfs_perag_put(pag);

		if (xchk_should_terminate(sc, &error))
			break;
	}

	if (error)
		return error;

	/*
	 * The global incore space reservation is taken from the incore
	 * counters, so leave that out of the computation.
	 */
	fsc->fdblocks -= mp->m_resblks_avail;

	/*
	 * Delayed allocation reservations are taken out of the incore counters
	 * but not recorded on disk, so leave them and their indlen blocks out
	 * of the computation.
	 */
	delayed = percpu_counter_sum(&mp->m_delalloc_blks);
	fsc->fdblocks -= delayed;

	trace_xchk_fscounters_calc(mp, fsc->icount, fsc->ifree, fsc->fdblocks,
			delayed);


	/* Bail out if the values we compute are totally nonsense. */
	if (fsc->icount < fsc->icount_min || fsc->icount > fsc->icount_max ||
	    fsc->fdblocks > mp->m_sb.sb_dblocks ||
	    fsc->ifree > fsc->icount_max)
		return -EFSCORRUPTED;

	/*
	 * If ifree > icount then we probably had some perturbation in the
	 * counters while we were calculating things.  We'll try a few times
	 * to maintain ifree <= icount before giving up.
	 */
	if (fsc->ifree > fsc->icount) {
		if (tries--)
			goto retry;
		xchk_set_incomplete(sc);
		return 0;
	}

	return 0;
}

/*
 * Is the @counter reasonably close to the @expected value?
 *
 * We neither locked nor froze anything in the filesystem while aggregating the
 * per-AG data to compute the @expected value, which means that the counter
 * could have changed.  We know the @old_value of the summation of the counter
 * before the aggregation, and we re-sum the counter now.  If the expected
 * value falls between the two summations, we're ok.
 *
 * Otherwise, we /might/ have a problem.  If the change in the summations is
 * more than we want to tolerate, the filesystem is probably busy and we should
 * just send back INCOMPLETE and see if userspace will try again.
 */
static inline bool
xchk_fscount_within_range(
	struct xfs_scrub	*sc,
	const int64_t		old_value,
	struct percpu_counter	*counter,
	uint64_t		expected)
{
	int64_t			min_value, max_value;
	int64_t			curr_value = percpu_counter_sum(counter);

	trace_xchk_fscounters_within_range(sc->mp, expected, curr_value,
			old_value);

	/* Negative values are always wrong. */
	if (curr_value < 0)
		return false;

	/* Exact matches are always ok. */
	if (curr_value == expected)
		return true;

	min_value = min(old_value, curr_value);
	max_value = max(old_value, curr_value);

	/* Within the before-and-after range is ok. */
	if (expected >= min_value && expected <= max_value)
		return true;

	/*
	 * If the difference between the two summations is too large, the fs
	 * might just be busy and so we'll mark the scrub incomplete.  Return
	 * true here so that we don't mark the counter corrupt.
	 *
	 * XXX: In the future when userspace can grant scrub permission to
	 * quiesce the filesystem to solve the outsized variance problem, this
	 * check should be moved up and the return code changed to signal to
	 * userspace that we need quiesce permission.
	 */
	if (max_value - min_value >= XCHK_FSCOUNT_MIN_VARIANCE) {
		xchk_set_incomplete(sc);
		return true;
	}

	return false;
}

/* Check the superblock counters. */
int
xchk_fscounters(
	struct xfs_scrub	*sc)
{
	struct xfs_mount	*mp = sc->mp;
	struct xchk_fscounters	*fsc = sc->buf;
	int64_t			icount, ifree, fdblocks;
	int			error;

	/* Snapshot the percpu counters. */
	icount = percpu_counter_sum(&mp->m_icount);
	ifree = percpu_counter_sum(&mp->m_ifree);
	fdblocks = percpu_counter_sum(&mp->m_fdblocks);

	/* No negative values, please! */
	if (icount < 0 || ifree < 0 || fdblocks < 0)
		xchk_set_corrupt(sc);

	/* See if icount is obviously wrong. */
	if (icount < fsc->icount_min || icount > fsc->icount_max)
		xchk_set_corrupt(sc);

	/* See if fdblocks is obviously wrong. */
	if (fdblocks > mp->m_sb.sb_dblocks)
		xchk_set_corrupt(sc);

	/*
	 * If ifree exceeds icount by more than the minimum variance then
	 * something's probably wrong with the counters.
	 */
	if (ifree > icount && ifree - icount > XCHK_FSCOUNT_MIN_VARIANCE)
		xchk_set_corrupt(sc);

	/* Walk the incore AG headers to calculate the expected counters. */
	error = xchk_fscount_aggregate_agcounts(sc, fsc);
	if (!xchk_process_error(sc, 0, XFS_SB_BLOCK(mp), &error))
		return error;
	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_INCOMPLETE)
		return 0;

	/* Compare the in-core counters with whatever we counted. */
	if (!xchk_fscount_within_range(sc, icount, &mp->m_icount, fsc->icount))
		xchk_set_corrupt(sc);

	if (!xchk_fscount_within_range(sc, ifree, &mp->m_ifree, fsc->ifree))
		xchk_set_corrupt(sc);

	if (!xchk_fscount_within_range(sc, fdblocks, &mp->m_fdblocks,
			fsc->fdblocks))
		xchk_set_corrupt(sc);

	return 0;
}