xfs: catch buffers written without verifiers attached

We recently had a bug where buffers were slipping through log
recovery without any verifier attached to them. This was resulting
in on-disk CRC mismatches for valid data. Add some warning code to
catch this occurrence so that we catch such bugs during development
rather than not being aware they exist.

Note that we cannot do this verification unconditionally as non-CRC
filesystems don't always attach verifiers to the buffers being
written. e.g. during log recovery we cannot identify all the
different types of buffers correctly on non-CRC filesystems, so we
can't attach the correct verifiers in all cases and so we don't
attach any. Hence we don't want on non-CRC filesystems to avoid
spamming the logs with false indications.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_buf.c

@@ -1330,6 +1330,20 @@ _xfs_buf_ioapply(
 						   SHUTDOWN_CORRUPT_INCORE);
 				return;
 			}
+		} else if (bp->b_bn != XFS_BUF_DADDR_NULL) {
+			struct xfs_mount *mp = bp->b_target->bt_mount;
+
+			/*
+			 * non-crc filesystems don't attach verifiers during
+			 * log recovery, so don't warn for such filesystems.
+			 */
+			if (xfs_sb_version_hascrc(&mp->m_sb)) {
+				xfs_warn(mp,
+					"%s: no ops on block 0x%llx/0x%x",
+					__func__, bp->b_bn, bp->b_length);
+				xfs_hex_dump(bp->b_addr, 64);
+				dump_stack();
+			}
 		}
 	} else if (bp->b_flags & XBF_READ_AHEAD) {
 		rw = READA;

fs/xfs/xfs_log.c

@@ -1369,8 +1369,14 @@ xlog_alloc_log(
 
 	xlog_get_iclog_buffer_size(mp, log);
 
+	/*
+	 * Use a NULL block for the extra log buffer used during splits so that
+	 * it will trigger errors if we ever try to do IO on it without first
+	 * having set it up properly.
+	 */
 	error = -ENOMEM;
-	bp = xfs_buf_alloc(mp->m_logdev_targp, 0, BTOBB(log->l_iclog_size), 0);
+	bp = xfs_buf_alloc(mp->m_logdev_targp, XFS_BUF_DADDR_NULL,
+			   BTOBB(log->l_iclog_size), 0);
 	if (!bp)
 		goto out_free_log;