xfs: always succeed at setting the reserve pool size

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>

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 3c6d9d6..5c2bea1 100644 (file)
--- 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) {