selftests/uffd: allow EINTR/EAGAIN

This allow test to continue with interruptions like gdb.

Link: https://lkml.kernel.org/r/20211115135219.85881-1-peterx@redhat.comSigned-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/userfaultfd.c

@@ -648,7 +648,7 @@ static int uffd_read_msg(int ufd, struct uffd_msg *msg)
 
 	if (ret != sizeof(*msg)) {
 		if (ret < 0) {
-			if (errno == EAGAIN)
+			if (errno == EAGAIN || errno == EINTR)
 				return 1;
 			err("blocking read error");
 		} else {
@@ -724,8 +724,11 @@ static void *uffd_poll_thread(void *arg)
 
 	for (;;) {
 		ret = poll(pollfd, 2, -1);
-		if (ret <= 0)
+		if (ret <= 0) {
+			if (errno == EINTR || errno == EAGAIN)
+				continue;
 			err("poll error: %d", ret);
+		}
 		if (pollfd[1].revents & POLLIN) {
 			if (read(pollfd[1].fd, &tmp_chr, 1) != 1)
 				err("read pipefd error");