xfs: don't trip over negative free space in xfs_reserve_blocks
If we somehow end up with a filesystem that has fewer free blocks than
the blocks set aside to avoid ENOSPC deadlocks, it's possible that the
free space calculation in xfs_reserve_blocks will spit out a negative
number (because percpu_counter_sum returns s64). We fail to notice
this negative number and set fdblks_delta to it. Now we increment
fdblocks(!) and the unsigned type of m_resblks means that we end up
setting a ridiculously huge m_resblks reservation.
Avoid this comedy of errors by detecting the negative free space and
returning -ENOSPC.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index a7afcad..3f2bd60 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -387,7 +387,7 @@ xfs_reserve_blocks(
do {
free = percpu_counter_sum(&mp->m_fdblocks) -
mp->m_alloc_set_aside;
- if (!free)
+ if (free <= 0)
break;
delta = request - mp->m_resblks;