xfs: don't deplete the reserve pool when trying to shrink the fs

Every now and then, xfs/168 fails with this logged in dmesg:

Reserve blocks depleted! Consider increasing reserve pool size.
EXPERIMENTAL online shrink feature in use. Use at your own risk!
Per-AG reservation for AG 1 failed.  Filesystem may run out of space.
Per-AG reservation for AG 1 failed.  Filesystem may run out of space.
Error -28 reserving per-AG metadata reserve pool.
Corruption of in-memory data (0x8) detected at xfs_ag_shrink_space+0x23c/0x3b0 [xfs] (fs/xfs/libxfs/xfs_ag.c:1007).  Shutting down filesystem.

It's silly to deplete the reserved blocks pool just to shrink the
filesystem, particularly since the fs goes down after that.

Fixes: fb2fc1720185 ("xfs: support shrinking unused space in the last AG")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 13851c0..5f00527 100644 (file)
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -140,9 +140,13 @@ xfs_growfs_data_private(
                return -EINVAL;
        }
 
-       error = xfs_trans_alloc(mp, &M_RES(mp)->tr_growdata,
-                       (delta > 0 ? XFS_GROWFS_SPACE_RES(mp) : -delta), 0,
-                       XFS_TRANS_RESERVE, &tp);
+       if (delta > 0)
+               error = xfs_trans_alloc(mp, &M_RES(mp)->tr_growdata,
+                               XFS_GROWFS_SPACE_RES(mp), 0, XFS_TRANS_RESERVE,
+                               &tp);
+       else
+               error = xfs_trans_alloc(mp, &M_RES(mp)->tr_growdata, -delta, 0,
+                               0, &tp);
        if (error)
                return error;