renameat(2): when retrying, check for pending signals

The vn_start_write() call there is already interruptible.  Check for
user signals before restarting due to ERELOOKUP, or after failed
vn_start_write().  Note that vn_start_write(V_XSLEEP | V_PCATCH)
does not check for signals if not sleeping.

PR:	295826
Reviewed by:	markj
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D57453

sys/kern/vfs_syscalls.c

@@ -3855,6 +3855,9 @@ kern_renameat(struct thread *td, int oldfd, const char *old, int newfd,
 			vfs_rel(tmp);
 			tmp = NULL;
 		}
+		error = sig_intr();
+		if (error != 0)
+			return (error);
 		error = vn_start_write(NULL, &mp, V_XSLEEP | V_PCATCH);
 		if (error != 0)
 			return (error);
@@ -3937,8 +3940,11 @@ kern_renameat(struct thread *td, int oldfd, const char *old, int newfd,
 out1:
 	if (error == ERESTART)
 		return (0);
-	if (error == ERELOOKUP)
-		goto again;
+	if (error == ERELOOKUP) {
+		error = sig_intr();
+		if (error == 0)
+			goto again;
+	}
 	return (error);
 }