Commit aafe12ce authored by Darrick J. Wong's avatar Darrick J. Wong
Browse files

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: default avatarDarrick J. Wong <>
Reviewed-by: default avatarAllison Henderson <>
Reviewed-by: default avatarChristoph Hellwig <>
parent 10ee2526
......@@ -387,7 +387,7 @@ xfs_reserve_blocks(
do {
free = percpu_counter_sum(&mp->m_fdblocks) -
if (!free)
if (free <= 0)
delta = request - mp->m_resblks;
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