linux-kernel - Re: block/blk-zoned.c:579:5-24: WARNING: atomic_dec_and_test variation before object free at line 583.

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Message-ID: <5b55417d-6b27-4186-bcfa-d6952624e99f@kernel.dk>
Date: Tue, 5 Nov 2024 08:56:40 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Christoph Hellwig <hch@....de>
Cc: kernel test robot <lkp@...el.com>, Damien Le Moal <dlemoal@...nel.org>,
 oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Hannes Reinecke <hare@...e.de>,
 "Martin K. Petersen" <martin.petersen@...cle.com>,
 Bart Van Assche <bvanassche@....org>
Subject: Re: block/blk-zoned.c:579:5-24: WARNING: atomic_dec_and_test
 variation before object free at line 583.

On 11/5/24 8:37 AM, Christoph Hellwig wrote:
> On Tue, Nov 05, 2024 at 08:36:33AM -0700, Jens Axboe wrote:
>> On 11/5/24 8:34 AM, Christoph Hellwig wrote:
>>> On Tue, Nov 05, 2024 at 06:52:25AM +0800, kernel test robot wrote:
>>>>>> block/blk-zoned.c:579:5-24: WARNING: atomic_dec_and_test variation before object free at line 583.
>>>
>>> Does anyone know what this warning is supposed to mean?
>>
>> It's supposed to mean "use refcount_t for things like this".
> 
> Have we finally resolved the performance problems with refcount_t for
> fast path operations?

I mean it's closer, but it's still slower. Will always be so. Does it
matter for zoned devices? Probably not.

I don't think it matters for this case. It's not like the ref itself is
something that is user controllable in terms of being able to get
anywhere near an overflow.

-- 
Jens Axboe