xfs: always assign buffer verifiers when one is provided

If a caller supplies buffer ops when trying to read a buffer and the
buffer doesn't already have buf ops assigned, ensure that the ops are
assigned to the buffer and the verifier is run on that buffer.

Note that current XFS code is careful to assign buffer ops after a
xfs_{trans_,}buf_read call in which ops were not supplied.  However, we
should apply ops defensively in case there is ever a coding mistake; and
an upcoming repair patch will need to be able to read a buffer without
assigning buf ops.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.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

@@ -749,6 +749,30 @@ _xfs_buf_read(
 	return xfs_buf_submit(bp);
 }
 
+/*
+ * If the caller passed in an ops structure and the buffer doesn't have ops
+ * assigned, set the ops and use them to verify the contents.  If the contents
+ * cannot be verified, we'll clear XBF_DONE.  We assume the buffer has no
+ * recorded errors and is already in XBF_DONE state.
+ */
+int
+xfs_buf_ensure_ops(
+	struct xfs_buf		*bp,
+	const struct xfs_buf_ops *ops)
+{
+	ASSERT(bp->b_flags & XBF_DONE);
+	ASSERT(bp->b_error == 0);
+
+	if (!ops || bp->b_ops)
+		return 0;
+
+	bp->b_ops = ops;
+	bp->b_ops->verify_read(bp);
+	if (bp->b_error)
+		bp->b_flags &= ~XBF_DONE;
+	return bp->b_error;
+}
+
 xfs_buf_t *
 xfs_buf_read_map(
 	struct xfs_buftarg	*target,
@@ -762,26 +786,32 @@ xfs_buf_read_map(
 	flags |= XBF_READ;
 
 	bp = xfs_buf_get_map(target, map, nmaps, flags);
-	if (bp) {
-		trace_xfs_buf_read(bp, flags, _RET_IP_);
+	if (!bp)
+		return NULL;
 
-		if (!(bp->b_flags & XBF_DONE)) {
-			XFS_STATS_INC(target->bt_mount, xb_get_read);
-			bp->b_ops = ops;
-			_xfs_buf_read(bp, flags);
-		} else if (flags & XBF_ASYNC) {
-			/*
-			 * Read ahead call which is already satisfied,
-			 * drop the buffer
-			 */
-			xfs_buf_relse(bp);
-			return NULL;
-		} else {
-			/* We do not want read in the flags */
-			bp->b_flags &= ~XBF_READ;
-		}
+	trace_xfs_buf_read(bp, flags, _RET_IP_);
+
+	if (!(bp->b_flags & XBF_DONE)) {
+		XFS_STATS_INC(target->bt_mount, xb_get_read);
+		bp->b_ops = ops;
+		_xfs_buf_read(bp, flags);
+		return bp;
+	}
+
+	xfs_buf_ensure_ops(bp, ops);
+
+	if (flags & XBF_ASYNC) {
+		/*
+		 * Read ahead call which is already satisfied,
+		 * drop the buffer
+		 */
+		xfs_buf_relse(bp);
+		return NULL;
 	}
 
+	/* We do not want read in the flags */
+	bp->b_flags &= ~XBF_READ;
+	ASSERT(bp->b_ops != NULL || ops == NULL);
 	return bp;
 }
 

fs/xfs/xfs_buf.h

@@ -385,4 +385,6 @@ extern int xfs_setsize_buftarg(xfs_buftarg_t *, unsigned int);
 #define xfs_getsize_buftarg(buftarg)	block_size((buftarg)->bt_bdev)
 #define xfs_readonly_buftarg(buftarg)	bdev_read_only((buftarg)->bt_bdev)
 
+int xfs_buf_ensure_ops(struct xfs_buf *bp, const struct xfs_buf_ops *ops);
+
 #endif	/* __XFS_BUF_H__ */

fs/xfs/xfs_trans_buf.c

@@ -264,11 +264,39 @@ xfs_trans_read_buf_map(
 			return -EIO;
 		}
 
+		/*
+		 * Check if the caller is trying to read a buffer that is
+		 * already attached to the transaction yet has no buffer ops
+		 * assigned.  Ops are usually attached when the buffer is
+		 * attached to the transaction, or by the read caller if
+		 * special circumstances.  That didn't happen, which is not
+		 * how this is supposed to go.
+		 *
+		 * If the buffer passes verification we'll let this go, but if
+		 * not we have to shut down.  Let the transaction cleanup code
+		 * release this buffer when it kills the tranaction.
+		 */
+		ASSERT(bp->b_ops != NULL);
+		error = xfs_buf_ensure_ops(bp, ops);
+		if (error) {
+			xfs_buf_ioerror_alert(bp, __func__);
+
+			if (tp->t_flags & XFS_TRANS_DIRTY)
+				xfs_force_shutdown(tp->t_mountp,
+						SHUTDOWN_META_IO_ERROR);
+
+			/* bad CRC means corrupted metadata */
+			if (error == -EFSBADCRC)
+				error = -EFSCORRUPTED;
+			return error;
+		}
+
 		bip = bp->b_log_item;
 		bip->bli_recur++;
 
 		ASSERT(atomic_read(&bip->bli_refcount) > 0);
 		trace_xfs_trans_read_buf_recur(bip);
+		ASSERT(bp->b_ops != NULL || ops == NULL);
 		*bpp = bp;
 		return 0;
 	}
@@ -316,6 +344,7 @@ xfs_trans_read_buf_map(
 		_xfs_trans_bjoin(tp, bp, 1);
 		trace_xfs_trans_read_buf(bp->b_log_item);
 	}
+	ASSERT(bp->b_ops != NULL || ops == NULL);
 	*bpp = bp;
 	return 0;