xfs: allow parent directory scans to be interrupted with fatal signals

Allow a fatal signal to interrupt us when we're scanning a directory to
verify a parent pointer.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/scrub/parent.c

@@ -32,8 +32,10 @@ xchk_setup_parent(
 
 struct xchk_parent_ctx {
 	struct dir_context	dc;
+	struct xfs_scrub	*sc;
 	xfs_ino_t		ino;
 	xfs_nlink_t		nlink;
+	bool			cancelled;
 };
 
 /* Look for a single entry in a directory pointing to an inode. */
@@ -47,11 +49,21 @@ xchk_parent_actor(
 	unsigned		type)
 {
 	struct xchk_parent_ctx	*spc;
+	int			error = 0;
 
 	spc = container_of(dc, struct xchk_parent_ctx, dc);
 	if (spc->ino == ino)
 		spc->nlink++;
-	return 0;
+
+	/*
+	 * If we're facing a fatal signal, bail out.  Store the cancellation
+	 * status separately because the VFS readdir code squashes error codes
+	 * into short directory reads.
+	 */
+	if (xchk_should_terminate(spc->sc, &error))
+		spc->cancelled = true;
+
+	return error;
 }
 
 /* Count the number of dentries in the parent dir that point to this inode. */
@@ -62,10 +74,9 @@ xchk_parent_count_parent_dentries(
 	xfs_nlink_t		*nlink)
 {
 	struct xchk_parent_ctx	spc = {
-		.dc.actor = xchk_parent_actor,
-		.dc.pos = 0,
-		.ino = sc->ip->i_ino,
-		.nlink = 0,
+		.dc.actor	= xchk_parent_actor,
+		.ino		= sc->ip->i_ino,
+		.sc		= sc,
 	};
 	size_t			bufsize;
 	loff_t			oldpos;
@@ -97,6 +108,10 @@ xchk_parent_count_parent_dentries(
 		error = xfs_readdir(sc->tp, parent, &spc.dc, bufsize);
 		if (error)
 			goto out;
+		if (spc.cancelled) {
+			error = -EAGAIN;
+			goto out;
+		}
 		if (oldpos == spc.dc.pos)
 			break;
 		oldpos = spc.dc.pos;