xfs: superblock scrub should use short-lived buffers

Secondary superblocks are rarely used, so create a helper to read a
given non-primary AG's superblock and ensure that it won't stick around
hogging memory.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

4 files changed, 27 insertions, 3 deletions

diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index d9b94bd5f689..d9bef41a3f26 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -972,3 +972,25 @@ xfs_fs_geometry(
 
         return 0;
 }
+
+/* Read a secondary superblock. */
+int
+xfs_sb_read_secondary(
+        struct xfs_mount        *mp,
+        struct xfs_trans        *tp,
+        xfs_agnumber_t          agno,
+        struct xfs_buf          **bpp)
+{
+        struct xfs_buf          *bp;
+        int                     error;
+
+        ASSERT(agno != 0 && agno != NULLAGNUMBER);
+        error = xfs_trans_read_buf(mp, tp, mp->m_ddev_targp,
+                        XFS_AG_DADDR(mp, agno, XFS_SB_BLOCK(mp)),
+                        XFS_FSS_TO_BB(mp, 1), 0, &bp, &xfs_sb_buf_ops);
+        if (error)
+                return error;
+        xfs_buf_set_ref(bp, XFS_SSB_REF);
+        *bpp = bp;
+        return 0;
+}
diff --git a/fs/xfs/libxfs/xfs_sb.h b/fs/xfs/libxfs/xfs_sb.h
index 63dcd2a1a657..5166d78b2c34 100644
--- a/fs/xfs/libxfs/xfs_sb.h
+++ b/fs/xfs/libxfs/xfs_sb.h
@@ -37,5 +37,8 @@ extern void	xfs_sb_quota_from_disk(struct xfs_sb *sbp);
 #define XFS_FS_GEOM_MAX_STRUCT_VER      (4)
 extern int      xfs_fs_geometry(struct xfs_sb *sbp, struct xfs_fsop_geom *geo,
                                 int struct_version);
+extern int      xfs_sb_read_secondary(struct xfs_mount *mp,
+                                struct xfs_trans *tp, xfs_agnumber_t agno,
+                                struct xfs_buf **bpp);
 
 #endif  /* __XFS_SB_H__ */
diff --git a/fs/xfs/libxfs/xfs_shared.h b/fs/xfs/libxfs/xfs_shared.h
index 8efc06e62b13..ae99c260adb1 100644
--- a/fs/xfs/libxfs/xfs_shared.h
+++ b/fs/xfs/libxfs/xfs_shared.h
@@ -112,6 +112,7 @@ void	xfs_log_get_max_trans_res(struct xfs_mount *mp,
 #define XFS_ATTR_BTREE_REF      1
 #define XFS_DQUOT_REF           1
 #define XFS_REFC_BTREE_REF      1
+#define XFS_SSB_REF             0
 
 /*
  * Flags for xfs_trans_ichgtime().
diff --git a/fs/xfs/scrub/agheader.c b/fs/xfs/scrub/agheader.c
index 08a1f013d92c..831acc0a328f 100644
--- a/fs/xfs/scrub/agheader.c
+++ b/fs/xfs/scrub/agheader.c
@@ -157,9 +157,7 @@ xfs_scrub_superblock(
         if (agno == 0)
                 return 0;
 
-        error = xfs_trans_read_buf(mp, sc->tp, mp->m_ddev_targp,
-                  XFS_AGB_TO_DADDR(mp, agno, XFS_SB_BLOCK(mp)),
-                  XFS_FSS_TO_BB(mp, 1), 0, &bp, &xfs_sb_buf_ops);
+        error = xfs_sb_read_secondary(mp, sc->tp, agno, &bp);
         /*
          * The superblock verifier can return several different error codes
          * if it thinks the superblock doesn't look right.  For a mount these