From: Darrick J. Wong <djwong@xxxxxxxxxx>
Don't spin in an infinite loop trying to reserve blocks -- if we can't
do it after 30 tries, we're racing with a nearly full filesystem, so
just give up.
Cc: Brian Foster <bfoster@xxxxxxxxxx>
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---
fs/xfs/xfs_fsops.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index b71799a3acd3..4076b9004077 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -379,6 +379,7 @@ xfs_reserve_blocks(
int64_t fdblks_delta = 0;
uint64_t request;
int64_t free;
+ unsigned int tries;
int error = 0;
/* If inval is null, report current values and return */
@@ -430,9 +431,16 @@ 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 loop body 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. We also
+ * cannot tell if @free remaining unchanged between iterations is due
+ * to an idle system or freed blocks being consumed immediately, so
+ * we'll try a finite number of times to satisfy the request.
*/
error = -ENOSPC;
- do {
+ for (tries = 0; tries < 30 && error == -ENOSPC; tries++) {
/*
* The reservation pool cannot take space that xfs_mod_fdblocks
* will not give us.
@@ -462,7 +470,7 @@ xfs_reserve_blocks(
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
