[PATCH] selftests/perf_events: Fix mmap() error check in sigtrap_threads

[Hongfu Li]

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.

Signed-off-by: Hongfu Li <lihon...@kylinos.cn>
---
 tools/testing/selftests/perf_events/watermark_signal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/perf_events/watermark_signal.c 
b/tools/testing/selftests/perf_events/watermark_signal.c
index 0f64b9b17081..a84709cabd8b 100644
--- 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;
        }
-- 
2.25.1