[PATCH 5.15 5/9] xfs: always succeed at setting the reserve pool size

From: Leah Rumancik <leah.rumancik@gmail.com>
To: stable@vger.kernel.org
Cc: linux-xfs@vger.kernel.org, amir73il@gmail.com,
	"Darrick J. Wong" <djwong@kernel.org>,
	Dave Chinner <dchinner@redhat.com>,
	Leah Rumancik <leah.rumancik@gmail.com>
Subject: [PATCH 5.15 5/9] xfs: always succeed at setting the reserve pool size
Date: Fri, 19 Aug 2022 11:14:27 -0700	[thread overview]
Message-ID: <20220819181431.4113819-6-leah.rumancik@gmail.com> (raw)
In-Reply-To: <20220819181431.4113819-1-leah.rumancik@gmail.com>

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>
---
 fs/xfs/xfs_fsops.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 3c6d9d6836ef..5c2bea1e12a8 100644
--- 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) {
-- 
2.37.1.595.g718a3a8f04-goog

