selftests/perf_events: fix mmap() error check in sigtrap_threads

In sigtrap_threads(), the return value of mmap() is checked against NULL.
mmap() returns MAP_FAILED, which is (void *)-1, not NULL, when it fails.
Since MAP_FAILED is non-zero and non-NULL, the condition "p == NULL" will
never be true on failure, causing the program to proceed with an invalid
pointer and segfault if mmap() actually fails under memory pressure.

Link: https://lore.kernel.org/20260513025838.594945-1-lihongfu@kylinos.cn
Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mickael Salaun <mic@digikod.net>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Kyle Huey <khuey@kylehuey.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/perf_events/watermark_signal.c b/tools/testing/selftests/perf_events/watermark_signal.c
index 0f64b9b170813cbd9662ea6b4eabf1c701fb3df5..a84709cabd8be9cda65b08e2a3b3a97b0d09fc17 100644 (file)
--- a/tools/testing/selftests/perf_events/watermark_signal.c
+++ b/tools/testing/selftests/perf_events/watermark_signal.c
@@ -102,7 +102,7 @@ TEST(watermark_signal)
        }
 
        p = mmap(NULL, 2 * page_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
-       if (p == NULL) {
+       if (p == MAP_FAILED) {
                perror("mmap");
                goto cleanup;
        }