xfs: perag initialization should only touch m_ag_max_usable for AG 0

BugLink: http://bugs.launchpad.net/bugs/1731951
commit 9789dd9e1d939232e8ff4c50ef8e75aa6781b3fb upstream.

We call __xfs_ag_resv_init to make a per-AG reservation for each AG.
This makes the reservation per-AG, not per-filesystem.  Therefore, it
is incorrect to adjust m_ag_max_usable for each AG.  Adjust it only
when we're reserving AG 0's blocks so that we only do it once per fs.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/fs/xfs/libxfs/xfs_ag_resv.c b/fs/xfs/libxfs/xfs_ag_resv.c
index b008ff3250eba4f3884e18841c4c316b7e7cbf50..df3e600835e8de81e69ac295b06fae6fecefd7a4 100644 (file)
--- a/fs/xfs/libxfs/xfs_ag_resv.c
+++ b/fs/xfs/libxfs/xfs_ag_resv.c
@@ -156,7 +156,8 @@ __xfs_ag_resv_free(
        trace_xfs_ag_resv_free(pag, type, 0);
 
        resv = xfs_perag_resv(pag, type);
-       pag->pag_mount->m_ag_max_usable += resv->ar_asked;
+       if (pag->pag_agno == 0)
+               pag->pag_mount->m_ag_max_usable += resv->ar_asked;
        /*
         * AGFL blocks are always considered "free", so whatever
         * was reserved at mount time must be given back at umount.
@@ -216,7 +217,14 @@ __xfs_ag_resv_init(
                return error;
        }
 
-       mp->m_ag_max_usable -= ask;
+       /*
+        * Reduce the maximum per-AG allocation length by however much we're
+        * trying to reserve for an AG.  Since this is a filesystem-wide
+        * counter, we only make the adjustment for AG 0.  This assumes that
+        * there aren't any AGs hungrier for per-AG reservation than AG 0.
+        */
+       if (pag->pag_agno == 0)
+               mp->m_ag_max_usable -= ask;
 
        resv = xfs_perag_resv(pag, type);
        resv->ar_asked = ask;