From: "Darrick J. Wong" djwong@kernel.org
[ Upstream commit c8c568259772751a14e969b7230990508de73d9d ]
xfs_reserve_blocks controls the size of the user-visible free space reserve pool. Given the difference between the current and requested pool sizes, it will try to reserve free space from fdblocks. However, the amount requested from fdblocks is also constrained by the amount of space that we think xfs_mod_fdblocks will give us. If we forget to subtract m_allocbt_blks before calling xfs_mod_fdblocks, it will will return ENOSPC and we'll hang the kernel at mount due to the infinite loop.
In commit fd43cf600cf6, we decided that xfs_mod_fdblocks should not hand out the "free space" used by the free space btrees, because some portion of the free space btrees hold in reserve space for future btree expansion. Unfortunately, xfs_reserve_blocks' estimation of the number of blocks that it could request from xfs_mod_fdblocks was not updated to include m_allocbt_blks, so if space is extremely low, the caller hangs.
Fix this by creating a function to estimate the number of blocks that can be reserved from fdblocks, which needs to exclude the set-aside and m_allocbt_blks.
Found by running xfs/306 (which formats a single-AG 20MB filesystem) with an fstests configuration that specifies a 1k blocksize and a specially crafted log size that will consume 7/8 of the space (17920 blocks, specifically) in that AG.
Cc: Brian Foster bfoster@redhat.com Fixes: fd43cf600cf6 ("xfs: set aside allocation btree blocks from block reservation") Signed-off-by: Darrick J. Wong djwong@kernel.org Reviewed-by: Brian Foster bfoster@redhat.com Reviewed-by: Dave Chinner dchinner@redhat.com Signed-off-by: Leah Rumancik leah.rumancik@gmail.com Acked-by: Darrick J. Wong djwong@kernel.org --- fs/xfs/xfs_fsops.c | 2 +- fs/xfs/xfs_mount.c | 2 +- fs/xfs/xfs_mount.h | 15 +++++++++++++++ 3 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c index 33e26690a8c4..710e857bb825 100644 --- a/fs/xfs/xfs_fsops.c +++ b/fs/xfs/xfs_fsops.c @@ -434,7 +434,7 @@ xfs_reserve_blocks( error = -ENOSPC; do { free = percpu_counter_sum(&mp->m_fdblocks) - - mp->m_alloc_set_aside; + xfs_fdblocks_unavailable(mp); if (free <= 0) break;
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c index 62f3c153d4b2..76056de83971 100644 --- a/fs/xfs/xfs_mount.c +++ b/fs/xfs/xfs_mount.c @@ -1132,7 +1132,7 @@ xfs_mod_fdblocks( * problems (i.e. transaction abort, pagecache discards, etc.) than * slightly premature -ENOSPC. */ - set_aside = mp->m_alloc_set_aside + atomic64_read(&mp->m_allocbt_blks); + set_aside = xfs_fdblocks_unavailable(mp); percpu_counter_add_batch(&mp->m_fdblocks, delta, batch); if (__percpu_counter_compare(&mp->m_fdblocks, set_aside, XFS_FDBLOCKS_BATCH) >= 0) { diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h index e091f3b3fa15..86564295fce6 100644 --- a/fs/xfs/xfs_mount.h +++ b/fs/xfs/xfs_mount.h @@ -478,6 +478,21 @@ extern void xfs_unmountfs(xfs_mount_t *); */ #define XFS_FDBLOCKS_BATCH 1024
+/* + * Estimate the amount of free space that is not available to userspace and is + * not explicitly reserved from the incore fdblocks. This includes: + * + * - The minimum number of blocks needed to support splitting a bmap btree + * - The blocks currently in use by the freespace btrees because they record + * the actual blocks that will fill per-AG metadata space reservations + */ +static inline uint64_t +xfs_fdblocks_unavailable( + struct xfs_mount *mp) +{ + return mp->m_alloc_set_aside + atomic64_read(&mp->m_allocbt_blks); +} + 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);