Re: [PATCH v2] selftests:mm: Fix mmap() error paths to check for MAP_FAILED

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On 8/22/24 17:30, Yang Ruibin wrote:
To correctly detect whether mmap is successful, must use if
(map_ptr == MAP_FAILED)to avoid incorrectly handling a valid
mapping.Fix mmap() error paths to check for MAP_FAILED.


Shouldn't you have written "avoid processing the return value
from a failed mmap" instead of "avoid incorrectly handling a
valid mapping", because !addr won't be a valid mapping? Also,
I guess it would be better to use ksft_exit_fail_perror(), but
I won't insist.


Signed-off-by: Yang Ruibin <11162571@xxxxxxxx>
---
  tools/testing/selftests/mm/ksm_tests.c     | 2 +-
  tools/testing/selftests/mm/madv_populate.c | 2 +-
  tools/testing/selftests/mm/soft-dirty.c    | 2 +-
  3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c
index b748c4890..dad54840f 100644
--- a/tools/testing/selftests/mm/ksm_tests.c
+++ b/tools/testing/selftests/mm/ksm_tests.c
@@ -201,7 +201,7 @@ static void  *allocate_memory(void *ptr, int prot, int mapping, char data, size_
  {
  	void *map_ptr = mmap(ptr, map_size, PROT_WRITE, mapping, -1, 0);
- if (!map_ptr) {
+	if (map_ptr == MAP_FAILED) {
  		perror("mmap");
  		return NULL;
  	}
diff --git a/tools/testing/selftests/mm/madv_populate.c b/tools/testing/selftests/mm/madv_populate.c
index ef7d911da..b89cb83ca 100644
--- a/tools/testing/selftests/mm/madv_populate.c
+++ b/tools/testing/selftests/mm/madv_populate.c
@@ -34,7 +34,7 @@ static void sense_support(void)
addr = mmap(0, pagesize, PROT_READ | PROT_WRITE,
  		    MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
-	if (!addr)
+	if (addr == MAP_FAILED)
  		ksft_exit_fail_msg("mmap failed\n");
ret = madvise(addr, pagesize, MADV_POPULATE_READ);
diff --git a/tools/testing/selftests/mm/soft-dirty.c b/tools/testing/selftests/mm/soft-dirty.c
index bdfa5d085..4ccbc053b 100644
--- a/tools/testing/selftests/mm/soft-dirty.c
+++ b/tools/testing/selftests/mm/soft-dirty.c
@@ -134,7 +134,7 @@ static void test_mprotect(int pagemap_fd, int pagesize, bool anon)
  	if (anon) {
  		map = mmap(NULL, pagesize, PROT_READ|PROT_WRITE,
  			   MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
-		if (!map)
+		if (map == MAP_FAILED)
  			ksft_exit_fail_msg("anon mmap failed\n");
  	} else {
  		test_fd = open(fname, O_RDWR | O_CREAT, 0664);




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