Re: [axboe-block:for-6.15/block 75/76] drivers/block/loop.c:388:6-25: WARNING: atomic_dec_and_test variation before object free at line 395.

[Jens Axboe <axboe@kernel.dk>]

On 3/23/25 6:36 PM, Ming Lei wrote:
> On Mon, Mar 24, 2025 at 06:52:22AM +0800, kernel test robot wrote:
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-6.15/block
>> head:   4c3f4bad7a6e9022489a9f8392f7147ed3ce74b1
>> commit: dfc77a934a3acdb13dadf237b7417c6a31b19da8 [75/76] loop: try to handle loop aio command via NOWAIT IO first
>> config: i386-randconfig-052-20250323 (https://download.01.org/0day-ci/archive/20250324/202503240625.LfSMQqA2-lkp@intel.com/config)
>> compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <lkp@intel.com>
>> | Closes: https://lore.kernel.org/oe-kbuild-all/202503240625.LfSMQqA2-lkp@intel.com/
>>
>> cocci warnings: (new ones prefixed by >>)
>>>> drivers/block/loop.c:388:6-25: WARNING: atomic_dec_and_test variation before object free at line 395.
> 
> The code itself is safe. Event through the atomic counter drops to zero,
> the object isn't freed, and the counter can be re-initialized & requeued
> internally.
> 
> This cocci rule should be 'wrong', or anyone can explain the exact risk
> here?

It's just a generic thing that it always reports, in case atomic_t is
used where a refcount_t would be "safer". You can just ignore it.

-- 
Jens Axboe