[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>

fs/xfs/linux-2.6/xfs_buf.c

@@ -997,7 +997,18 @@ xfs_buf_iodone_work(
 	xfs_buf_t		*bp =
 		container_of(work, xfs_buf_t, b_iodone_work);
 
-	if (bp->b_iodone)
+	/*
+	 * We can get an EOPNOTSUPP to ordered writes.  Here we clear the
+	 * ordered flag and reissue them.  Because we can't tell the higher
+	 * layers directly that they should not issue ordered I/O anymore, they
+	 * need to check if the ordered flag was cleared during I/O completion.
+	 */
+	if ((bp->b_error == EOPNOTSUPP) &&
+	    (bp->b_flags & (XBF_ORDERED|XBF_ASYNC)) == (XBF_ORDERED|XBF_ASYNC)) {
+		XB_TRACE(bp, "ordered_retry", bp->b_iodone);
+		bp->b_flags &= ~XBF_ORDERED;
+		xfs_buf_iorequest(bp);
+	} else if (bp->b_iodone)
 		(*(bp->b_iodone))(bp);
 	else if (bp->b_flags & XBF_ASYNC)
 		xfs_buf_relse(bp);

fs/xfs/linux-2.6/xfs_super.c

@@ -304,14 +304,6 @@ xfs_mountfs_check_barriers(xfs_mount_t *mp)
 		return;
 	}
 
-	if (mp->m_ddev_targp->bt_bdev->bd_disk->queue->ordered ==
-					QUEUE_ORDERED_NONE) {
-		xfs_fs_cmn_err(CE_NOTE, mp,
-		  "Disabling barriers, not supported by the underlying device");
-		mp->m_flags &= ~XFS_MOUNT_BARRIER;
-		return;
-	}
-
 	if (xfs_readonly_buftarg(mp->m_ddev_targp)) {
 		xfs_fs_cmn_err(CE_NOTE, mp,
 		  "Disabling barriers, underlying device is readonly");

fs/xfs/xfs_log.c

@@ -948,6 +948,19 @@ 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.
 	 */