[XFS] Barriers need to be dynamically checked and switched off

If the underlying block device suddenly stops supporting barriers, we need
to handle the -EOPNOTSUPP error in a sane manner rather than shutting
down the filesystem. If we get this error, clear the barrier flag, reissue
the I/O, and tell the world bad things are occurring.

SGI-PV: 964544
SGI-Modid: xfs-linux-melb:xfs-kern:28568a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tim Shimmin <tes@sgi.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 9bfb69e1e885..db09e1ea5cf3 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -949,6 +949,19 @@ xlog_iodone(xfs_buf_t *bp)
         l = iclog->ic_log;
 
         /*
+         * If the ordered flag has been removed by a lower
+         * layer, it means the underlyin device no longer supports
+         * barrier I/O. Warn loudly and turn off barriers.
+         */
+        if ((l->l_mp->m_flags & XFS_MOUNT_BARRIER) && !XFS_BUF_ORDERED(bp)) {
+                l->l_mp->m_flags &= ~XFS_MOUNT_BARRIER;
+                xfs_fs_cmn_err(CE_WARN, l->l_mp,
+                                "xlog_iodone: Barriers are no longer supported"
+                                " by device. Disabling barriers\n");
+                xfs_buftrace("XLOG_IODONE BARRIERS OFF", bp);
+        }
+
+        /*
          * Race to shutdown the filesystem if we see an error.
          */
         if (XFS_TEST_ERROR((XFS_BUF_GETERROR(bp)), l->l_mp,