On Wed, Oct 23, 2024 at 05:24:40PM +0100, Lorenzo Stoakes wrote:

Implement a new lightweight guard page feature, that is regions of userland
virtual memory that, when accessed, cause a fatal signal to arise.

<snip>

Hi Andrew - Could you apply the below fix-patch? I realise we must handle
fatal signals and conditional rescheduling in the vector_madvise() special
case.

Thanks!

----8<----
From 546d7e1831c71599fc733d589e0d75f52e84826d Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <redacted>
Date: Fri, 25 Oct 2024 18:05:48 +0100
Subject: [PATCH] mm: yield on fatal signal/cond_sched() in vector_madvise()

While we have to treat -ERESTARTNOINTR specially here as we are looping
through a vector of operations and can't simply restart the entire
operation, we mustn't hold up fatal signals or RT kernels.
---
 mm/madvise.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 48eba25e25fe..127aa5d86656 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c

@@ -1713,8 +1713,14 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
 		 * we have already rescinded locks, it should be no problem to
 		 * simply try again.
 		 */
-		if (ret == -ERESTARTNOINTR)
+		if (ret == -ERESTARTNOINTR) {
+			if (fatal_signal_pending(current)) {
+				ret = -EINTR;
+				break;
+			}
+			cond_resched();
 			continue;
+		}
 		if (ret < 0)
 			break;
 		iov_iter_advance(iter, iter_iov_len(iter));
--

2.47.0