[Devel] [PATCH vz10] selftests/filelock: zero-initialize struct flock

[Vasileios Almpanis]

Reviewed-by: Vasileios Almpanis <vasileios.almpanis at virtuozzo.com>

On 6/25/26 12:42 AM, Eva Kurchatova wrote:
> The ofdlocks test installs an OFD read lock at offset 5..7 and then
> issues two F_OFD_GETLK queries (one starting at offset 5 with length 1,
> one starting at offset 0 with length 0) expecting them to report the
> same lock. It then compares the two struct flock results with memcmp().
>
> Because 'fl' and 'fl2' live on the stack and are only partially
> initialized by the caller (l_type, l_whence, l_start, l_len, l_pid),
> the implicit padding bytes that 'struct flock' has on x86_64 are left
> with whatever happens to be on the stack. The kernel does not touch
> those padding bytes on the F_OFD_GETLK return path, so memcmp() of the
> full sizeof(struct flock) compares uninitialized padding from two
> different stack frames and intermittently reports them as different:
>
>    [SUCCESS] F_UNLCK test returns: locked, type 0 pid -1 len 3
>    [FAIL]    F_UNLCK test returns: locked, type 0 pid -1 len 3
>
> i.e. the printed fields are identical but memcmp() still fails.
>
> Zero-initialize both structs at declaration so the padding is
> deterministic and the comparison is meaningful.
>
> Signed-off-by: Eva Kurchatova <eva.kurchatova at virtuozzo.com>
>
> https://virtuozzo.atlassian.net/browse/VSTOR-134203
> Feature: fix selftests
>
> ---
>   tools/testing/selftests/filelock/ofdlocks.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/filelock/ofdlocks.c b/tools/testing/selftests/filelock/ofdlocks.c
> index a55b79810ab2..45dc417dae89 100644
> --- a/tools/testing/selftests/filelock/ofdlocks.c
> +++ b/tools/testing/selftests/filelock/ofdlocks.c
> @@ -35,7 +35,7 @@ static int lock_get(int fd, struct flock *fl)
>   int main(void)
>   {
>   	int rc;
> -	struct flock fl, fl2;
> +	struct flock fl = {0}, fl2 = {0};
>   	int fd = open("/tmp/aa", O_RDWR | O_CREAT | O_EXCL, 0600);
>   	int fd2 = open("/tmp/aa", O_RDONLY);
>   

-- 
Best regards, Vasileios Almpanis
Software Developer, Virtuozzo.