diff options
author | Darrick J. Wong <djwong@kernel.org> | 2022-03-11 10:56:01 -0800 |
---|---|---|
committer | Darrick J. Wong <djwong@kernel.org> | 2022-03-28 08:38:50 -0700 |
commit | 15f04fdc75aaaa1cccb0b8b3af1be290e118a7bc (patch) | |
tree | 2475bfcd29f3af97d83f17dbac636e5e24449fa6 /fs | |
parent | c8c568259772751a14e969b7230990508de73d9d (diff) |
xfs: remove infinite loop when reserving free block pool
Infinite loops in kernel code are scary. Calls to xfs_reserve_blocks
should be rare (people should just use the defaults!) so we really don't
need to try so hard. Simplify the logic here by removing the infinite
loop.
Cc: Brian Foster <bfoster@redhat.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/xfs/xfs_fsops.c | 50 |
1 files changed, 20 insertions, 30 deletions
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c index 710e857bb825..3c6d9d6836ef 100644 --- a/fs/xfs/xfs_fsops.c +++ b/fs/xfs/xfs_fsops.c @@ -430,46 +430,36 @@ xfs_reserve_blocks( * If the request is larger than the current reservation, reserve the * blocks before we update the reserve counters. Sample m_fdblocks and * perform a partial reservation if the request exceeds free space. + * + * The code below estimates how many blocks it can request from + * fdblocks to stash in the reserve pool. This is a classic TOCTOU + * race since fdblocks updates are not always coordinated via + * m_sb_lock. */ - error = -ENOSPC; - do { - free = percpu_counter_sum(&mp->m_fdblocks) - + free = percpu_counter_sum(&mp->m_fdblocks) - xfs_fdblocks_unavailable(mp); - if (free <= 0) - break; - - delta = request - mp->m_resblks; - lcounter = free - delta; - if (lcounter < 0) - /* We can't satisfy the request, just get what we can */ - fdblks_delta = free; - else - fdblks_delta = delta; - + delta = request - mp->m_resblks; + if (delta > 0 && free > 0) { /* * We'll either succeed in getting space from the free block - * count or we'll get an ENOSPC. If we get a ENOSPC, it means - * things changed while we were calculating fdblks_delta and so - * we should try again to see if there is anything left to - * reserve. - * - * Don't set the reserved flag here - we don't want to reserve - * the extra reserve blocks from the reserve..... + * count or we'll get an ENOSPC. Don't set the reserved flag + * here - we don't want to reserve the extra reserve blocks + * from the reserve. */ + fdblks_delta = min(free, delta); spin_unlock(&mp->m_sb_lock); error = xfs_mod_fdblocks(mp, -fdblks_delta, 0); spin_lock(&mp->m_sb_lock); - } while (error == -ENOSPC); - /* - * Update the reserve counters if blocks have been successfully - * allocated. - */ - if (!error && fdblks_delta) { - mp->m_resblks += fdblks_delta; - mp->m_resblks_avail += fdblks_delta; + /* + * Update the reserve counters if blocks have been successfully + * allocated. + */ + if (!error) { + mp->m_resblks += fdblks_delta; + mp->m_resblks_avail += fdblks_delta; + } } - out: if (outval) { outval->resblks = mp->m_resblks; |