From: Darrick J. Wong djwong@kernel.org
commit 15f04fdc75aaaa1cccb0b8b3af1be290e118a7bc upstream.
[Added wrapper xfs_fdblocks_unavailable() for 5.10.y backport]
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 Signed-off-by: Amir Goldstein amir73il@gmail.com Acked-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/xfs/xfs_fsops.c | 52 +++++++++++++++++++++------------------------------- fs/xfs/xfs_mount.h | 8 ++++++++ 2 files changed, 29 insertions(+), 31 deletions(-)
--- a/fs/xfs/xfs_fsops.c +++ b/fs/xfs/xfs_fsops.c @@ -376,46 +376,36 @@ 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) - - mp->m_alloc_set_aside; - 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; - + free = percpu_counter_sum(&mp->m_fdblocks) - + xfs_fdblocks_unavailable(mp); + 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; --- a/fs/xfs/xfs_mount.h +++ b/fs/xfs/xfs_mount.h @@ -406,6 +406,14 @@ extern int xfs_initialize_perag(xfs_moun xfs_agnumber_t *maxagi); extern void xfs_unmountfs(xfs_mount_t *);
+/* Accessor added for 5.10.y backport */ +static inline uint64_t +xfs_fdblocks_unavailable( + struct xfs_mount *mp) +{ + return mp->m_alloc_set_aside; +} + extern int xfs_mod_fdblocks(struct xfs_mount *mp, int64_t delta, bool reserved); extern int xfs_mod_frextents(struct xfs_mount *mp, int64_t delta);