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

[Pavel Tikhomirov]

Reviewed-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>

On 6/25/26 09:46, Vasileios Almpanis wrote:
> 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, Pavel Tikhomirov
Senior Software Developer, Virtuozzo.