selftests/mm: Fix mmap() return value check in run_migration_benchmark

[PATCH] selftests/mm: Fix mmap() return value check in run_migration_benchmark

Posted by Hongfu Li 1 month ago

mmap() returns MAP_FAILED on error, not NULL.  The current check uses
!buffer->ptr, which evaluates to false when mmap() fails (since
MAP_FAILED is (void *)-1, not 0), so the error path is never taken.

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

diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
index 788689497e92..d72adba5c74e 100644
--- a/tools/testing/selftests/mm/hmm-tests.c
+++ b/tools/testing/selftests/mm/hmm-tests.c
@@ -2688,7 +2688,7 @@ static inline int run_migration_benchmark(int fd, int use_thp, size_t buffer_siz
 	buffer->ptr = mmap(NULL, buffer_size, PROT_READ | PROT_WRITE,
 			  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 
-	if (!buffer->ptr)
+	if (buffer->ptr == MAP_FAILED)
 		return -1;
 
 	/* Apply THP hint if requested */
-- 
2.25.1

Re: [PATCH] selftests/mm: Fix mmap() return value check in run_migration_benchmark

Posted by SeongJae Park 1 month ago

On Tue, 12 May 2026 18:13:05 +0800 Hongfu Li <lihongfu@kylinos.cn> wrote:

> mmap() returns MAP_FAILED on error, not NULL.  The current check uses
> !buffer->ptr, which evaluates to false when mmap() fails (since
> MAP_FAILED is (void *)-1, not 0), so the error path is never taken.

Good catch, thank you!

> 
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH] selftests/mm: Fix mmap() return value check in run_migration_benchmark

Posted by Lorenzo Stoakes 1 month ago

On Tue, May 12, 2026 at 06:13:05PM +0800, Hongfu Li wrote:
> mmap() returns MAP_FAILED on error, not NULL.  The current check uses
> !buffer->ptr, which evaluates to false when mmap() fails (since
> MAP_FAILED is (void *)-1, not 0), so the error path is never taken.
>
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>

> ---
>  tools/testing/selftests/mm/hmm-tests.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index 788689497e92..d72adba5c74e 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -2688,7 +2688,7 @@ static inline int run_migration_benchmark(int fd, int use_thp, size_t buffer_siz
>  	buffer->ptr = mmap(NULL, buffer_size, PROT_READ | PROT_WRITE,
>  			  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>
> -	if (!buffer->ptr)
> +	if (buffer->ptr == MAP_FAILED)
>  		return -1;
>
>  	/* Apply THP hint if requested */
> --
> 2.25.1
>

Re: [PATCH] selftests/mm: Fix mmap() return value check in run_migration_benchmark

Posted by Donet Tom 1 month ago

On 5/12/26 3:43 PM, Hongfu Li wrote:
> mmap() returns MAP_FAILED on error, not NULL.  The current check uses
> !buffer->ptr, which evaluates to false when mmap() fails (since
> MAP_FAILED is (void *)-1, not 0), so the error path is never taken.
>
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>


LGTM

Reviewed-by: Donet Tom <donettom@linux.ibm.com>

> ---
>   tools/testing/selftests/mm/hmm-tests.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index 788689497e92..d72adba5c74e 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -2688,7 +2688,7 @@ static inline int run_migration_benchmark(int fd, int use_thp, size_t buffer_siz
>   	buffer->ptr = mmap(NULL, buffer_size, PROT_READ | PROT_WRITE,
>   			  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>   
> -	if (!buffer->ptr)
> +	if (buffer->ptr == MAP_FAILED)
>   		return -1;
>   
>   	/* Apply THP hint if requested */

Re: [PATCH] selftests/mm: Fix mmap() return value check in run_migration_benchmark

Posted by Mike Rapoport 1 month ago

On Tue, May 12, 2026 at 06:13:05PM +0800, Hongfu Li wrote:
> mmap() returns MAP_FAILED on error, not NULL.  The current check uses
> !buffer->ptr, which evaluates to false when mmap() fails (since
> MAP_FAILED is (void *)-1, not 0), so the error path is never taken.
> 
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
>  tools/testing/selftests/mm/hmm-tests.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index 788689497e92..d72adba5c74e 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -2688,7 +2688,7 @@ static inline int run_migration_benchmark(int fd, int use_thp, size_t buffer_siz
>  	buffer->ptr = mmap(NULL, buffer_size, PROT_READ | PROT_WRITE,
>  			  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>  
> -	if (!buffer->ptr)
> +	if (buffer->ptr == MAP_FAILED)
>  		return -1;
>  
>  	/* Apply THP hint if requested */
> -- 
> 2.25.1
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH] selftests/mm: Fix mmap() return value check in run_migration_benchmark

Posted by Dev Jain 1 month ago


On 12/05/26 3:43 pm, Hongfu Li wrote:
> mmap() returns MAP_FAILED on error, not NULL.  The current check uses
> !buffer->ptr, which evaluates to false when mmap() fails (since
> MAP_FAILED is (void *)-1, not 0), so the error path is never taken.
> 
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
> ---

Reviewed-by: Dev Jain <dev.jain@arm.com>

>  tools/testing/selftests/mm/hmm-tests.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index 788689497e92..d72adba5c74e 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -2688,7 +2688,7 @@ static inline int run_migration_benchmark(int fd, int use_thp, size_t buffer_siz
>  	buffer->ptr = mmap(NULL, buffer_size, PROT_READ | PROT_WRITE,
>  			  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>  
> -	if (!buffer->ptr)
> +	if (buffer->ptr == MAP_FAILED)
>  		return -1;
>  
>  	/* Apply THP hint if requested */

Re: [PATCH] selftests/mm: Fix mmap() return value check in run_migration_benchmark

Posted by David Hildenbrand (Arm) 1 month ago

On 5/12/26 12:13, Hongfu Li wrote:
> mmap() returns MAP_FAILED on error, not NULL.  The current check uses
> !buffer->ptr, which evaluates to false when mmap() fails (since
> MAP_FAILED is (void *)-1, not 0), so the error path is never taken.
> 
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
> ---
>  tools/testing/selftests/mm/hmm-tests.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index 788689497e92..d72adba5c74e 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -2688,7 +2688,7 @@ static inline int run_migration_benchmark(int fd, int use_thp, size_t buffer_siz
>  	buffer->ptr = mmap(NULL, buffer_size, PROT_READ | PROT_WRITE,
>  			  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>  
> -	if (!buffer->ptr)
> +	if (buffer->ptr == MAP_FAILED)
>  		return -1;
>  
>  	/* Apply THP hint if requested */


Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David