linux/fs/xfs/scrub/fscounters.c

367 lines
10 KiB
C

// 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_defer.h"
#include "xfs_btree.h"
#include "xfs_bit.h"
#include "xfs_log_format.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_inode.h"
#include "xfs_alloc.h"
#include "xfs_ialloc.h"
#include "xfs_rmap.h"
#include "xfs_error.h"
#include "xfs_errortag.h"
#include "xfs_icache.h"
#include "xfs_health.h"
#include "xfs_bmap.h"
#include "scrub/xfs_scrub.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;
error = -ENOMEM;
if (!agf_bp || !agi_bp)
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 (fatal_signal_pending(current))
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), KM_SLEEP);
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;
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 (fatal_signal_pending(current))
break;
}
/*
* 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;
}