linux-kernel - [PATCH] selftests/mm: Reduce uffd-unit-test poison test to minimum

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Message-ID: <20250620150058.1729489-1-peterx@redhat.com>
Date: Fri, 20 Jun 2025 11:00:58 -0400
From: Peter Xu <peterx@...hat.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	peterx@...hat.com,
	Ujwal Kundur <ujwal.kundur@...il.com>,
	David Hildenbrand <david@...hat.com>,
	shuah@...nel.org,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	jackmanb@...gle.com
Subject: [PATCH] selftests/mm: Reduce uffd-unit-test poison test to minimum

The test will still generate quite some unwanted MCE error messages to
syslog.  There was old proposal ratelimiting the MCE messages from kernel,
but that has risk of hiding real useful information on production systems.

We can at least reduce the test to minimum to not over-pollute dmesg,
however trying to not lose its coverage too much.

Cc: Axel Rasmussen <axelrasmussen@...gle.com>
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 tools/testing/selftests/mm/uffd-unit-tests.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index c73fd5d455c8..39b3fd1b7bf2 100644
--- a/tools/testing/selftests/mm/uffd-unit-tests.c
+++ b/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -1027,6 +1027,9 @@ static void uffd_poison_handle_fault(
 		do_uffdio_poison(uffd, offset);
 }
 
+/* Make sure to cover odd/even, and minimum duplications */
+#define  UFFD_POISON_TEST_NPAGES  4
+
 static void uffd_poison_test(uffd_test_args_t *targs)
 {
 	pthread_t uffd_mon;
@@ -1034,12 +1037,17 @@ static void uffd_poison_test(uffd_test_args_t *targs)
 	struct uffd_args args = { 0 };
 	struct sigaction act = { 0 };
 	unsigned long nr_sigbus = 0;
-	unsigned long nr;
+	unsigned long nr, poison_pages = UFFD_POISON_TEST_NPAGES;
+
+	if (nr_pages < poison_pages) {
+		uffd_test_skip("Too less pages for POISON test");
+		return;
+	}
 
 	fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
 
-	uffd_register_poison(uffd, area_dst, nr_pages * page_size);
-	memset(area_src, 0, nr_pages * page_size);
+	uffd_register_poison(uffd, area_dst, poison_pages * page_size);
+	memset(area_src, 0, poison_pages * page_size);
 
 	args.handle_fault = uffd_poison_handle_fault;
 	if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
@@ -1051,7 +1059,7 @@ static void uffd_poison_test(uffd_test_args_t *targs)
 	if (sigaction(SIGBUS, &act, 0))
 		err("sigaction");
 
-	for (nr = 0; nr < nr_pages; ++nr) {
+	for (nr = 0; nr < poison_pages; ++nr) {
 		unsigned long offset = nr * page_size;
 		const char *bytes = (const char *) area_dst + offset;
 		const char *i;
@@ -1078,9 +1086,9 @@ static void uffd_poison_test(uffd_test_args_t *targs)
 	if (pthread_join(uffd_mon, NULL))
 		err("pthread_join()");
 
-	if (nr_sigbus != nr_pages / 2)
+	if (nr_sigbus != poison_pages / 2)
 		err("expected to receive %lu SIGBUS, actually received %lu",
-		    nr_pages / 2, nr_sigbus);
+		    poison_pages / 2, nr_sigbus);
 
 	uffd_test_pass();
 }
-- 
2.49.0