From: Lorenzo Stoakes <ljs@kernel.org>
To: Hongfu Li <lihongfu@kylinos.cn>
Cc: akpm@linux-foundation.org, david@kernel.org, liam@infradead.org,
vbabka@kernel.org, rppt@kernel.org, surenb@google.com,
mhocko@suse.com, shuah@kernel.org, linux-mm@kvack.org,
linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] selftests/mm: Fix incorrect mmap() error handling with NULL instead of MAP_FAILED
Date: Wed, 13 May 2026 10:25:33 +0100 [thread overview]
Message-ID: <agRDVWDvId9Jx9Q0@lucifer> (raw)
In-Reply-To: <20260513025223.592766-1-lihongfu@kylinos.cn>
On Wed, May 13, 2026 at 10:52:23AM +0800, Hongfu Li wrote:
> mmap() returns MAP_FAILED, which is defined as (void *)-1, on error,
> not NULL. Several selftests incorrectly check the return value of
> mmap() using !ptr or ptr == NULL, which would erroneously treat
> MAP_FAILED as a valid pointer since MAP_FAILED is non-zero and
> non-NULL. This can lead to segfaults when mmap() actually fails
> under memory pressure.
>
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
Ugh how did we end up with all of these :) thanks for the fix, assuming you get
all of the other cases on respin, feel free to attach my tag to that:
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Cheers, Lorenzo
> ---
> tools/testing/selftests/mm/ksm_tests.c | 2 +-
> tools/testing/selftests/mm/madv_populate.c | 2 +-
> tools/testing/selftests/mm/soft-dirty.c | 4 ++--
> tools/testing/selftests/mm/vm_util.c | 2 +-
> 4 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/ksm_tests.c b/tools/testing/selftests/mm/ksm_tests.c
> index a0b48b839d54..ed481f817282 100644
> --- a/tools/testing/selftests/mm/ksm_tests.c
> +++ b/tools/testing/selftests/mm/ksm_tests.c
> @@ -174,7 +174,7 @@ 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 88050e0f829a..7fce5d0b622b 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 bcfcac99b436..67c26c265880 100644
> --- a/tools/testing/selftests/mm/soft-dirty.c
> +++ b/tools/testing/selftests/mm/soft-dirty.c
> @@ -143,7 +143,7 @@ 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);
> @@ -155,7 +155,7 @@ static void test_mprotect(int pagemap_fd, int pagesize, bool anon)
> ftruncate(test_fd, pagesize);
> map = mmap(NULL, pagesize, PROT_READ|PROT_WRITE,
> MAP_SHARED, test_fd, 0);
> - if (!map)
> + if (map == MAP_FAILED)
> ksft_exit_fail_msg("file mmap failed\n");
> }
>
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index db94564f4431..63aaa2d9ec0b 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -463,7 +463,7 @@ bool softdirty_supported(void)
> /* New mappings are expected to be marked with VM_SOFTDIRTY (sd). */
> 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");
>
> supported = check_vmflag(addr, "sd");
> --
> 2.25.1
>
prev parent reply other threads:[~2026-05-13 9:25 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-13 2:52 [PATCH] selftests/mm: Fix incorrect mmap() error handling with NULL instead of MAP_FAILED Hongfu Li
2026-05-13 4:27 ` Dev Jain
2026-05-13 9:09 ` Hongfu Li
2026-05-13 9:25 ` Lorenzo Stoakes [this message]
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