[PATCH 5.15 240/244] xfs: always succeed at setting the reserve pool size

Greg Kroah-Hartman
2022-08-23T10:30:02Z

From: "Darrick J. Wong" <djwong@kernel.org>

[ Upstream commit 0baa2657dc4d79202148be79a3dc36c35f425060 ]

Nowadays, xfs_mod_fdblocks will always choose to fill the reserve pool
with freed blocks before adding to fdblocks. Therefore, we can change
the behavior of xfs_reserve_blocks slightly -- setting the target size
of the pool should always succeed, since a deficiency will eventually
be made up as blocks get freed.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/xfs/xfs_fsops.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -434,11 +434,14 @@ xfs_reserve_blocks(
* 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.
+ * m_sb_lock. Set the reserve size even if there's not enough free
+ * space to fill it because mod_fdblocks will refill an undersized
+ * reserve when it can.
*/
free = percpu_counter_sum(&mp->m_fdblocks) -
xfs_fdblocks_unavailable(mp);
delta = request - mp->m_resblks;
+ mp->m_resblks = request;
if (delta > 0 && free > 0) {
/*
* We'll either succeed in getting space from the free block
@@ -455,10 +458,8 @@ xfs_reserve_blocks(
* Update the reserve counters if blocks have been successfully
* allocated.
*/
- if (!error) {
- mp->m_resblks += fdblks_delta;
+ if (!error)
mp->m_resblks_avail += fdblks_delta;
- }
}
out:
if (outval) {