Re: [kbuild-all] Re: [song-md:md-next 5/6] drivers/md/raid10.c:1526:8-27: atomic_dec_and_test variation before object free at line 1532.

[Rong Chen <rong.a.chen@intel.com>]

On 3/16/21 2:56 PM, Song Liu wrote:
>
>> On Mar 15, 2021, at 7:29 PM, Xiao Ni <xni@redhat.com> wrote:
>>
>> Hi all
>>
>> The atomic_t r10_bio->remaining starts at 1 in raid10_handle_discard. It means
>> raid10_handle_discard uses it and sets it to 1. So in fact it starts at 0 and sets to 1
>> when it's used at first time. Then r10_bio->remaining is added by atomic_inc per usage.
>>
>> It decrements the value when leaving raid10_handle_discard and in every callback function.
>> So the count of r10_bio->remaining in this patch is right.
>>
>> Regards
>> Xiao
> It does look like a false alarm, as we set r10bio to first_r10bio after
> the free.
>
> Thanks,
> Song

Hi all,

Thanks for the clarification, we have disabled such warning.

Best Regards,
Rong Chen

>
>> On 03/16/2021 08:29 AM, kernel test robot wrote:
>>> tree:   git://git.kernel.org/pub/scm/linux/kernel/git/song/md.git md-next
>>> head:   49c4d345c81f149a29b3db6e521e5191e55f02b6
>>> commit: f3cf8c2b2caf6ae77b7c786218d3b060faef63a6 [5/6] md/raid10: improve discard request for far layout
>>> config: x86_64-allyesconfig (attached as .config)
>>> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
>>>
>>> If you fix the issue, kindly add following tag as appropriate
>>> Reported-by: kernel test robot <lkp@intel.com>
>>>
>>>
>>> "coccinelle warnings: (new ones prefixed by >>)"
>>>>> drivers/md/raid10.c:1526:8-27: atomic_dec_and_test variation before object free at line 1532.
>>>     drivers/md/raid10.c:1526:8-27: atomic_dec_and_test variation before object free at line 1537.
>>>
>>> vim +1526 drivers/md/raid10.c
>>>
>>>    1520	
>>>    1521	static void raid_end_discard_bio(struct r10bio *r10bio)
>>>    1522	{
>>>    1523		struct r10conf *conf = r10bio->mddev->private;
>>>    1524		struct r10bio *first_r10bio;
>>>    1525	
>>>> 1526		while (atomic_dec_and_test(&r10bio->remaining)) {
>>>    1527	
>>>    1528			allow_barrier(conf);
>>>    1529	
>>>    1530			if (!test_bit(R10BIO_Discard, &r10bio->state)) {
>>>    1531				first_r10bio = (struct r10bio *)r10bio->master_bio;
>>>> 1532				free_r10bio(r10bio);
>>>    1533				r10bio = first_r10bio;
>>>    1534			} else {
>>>    1535				md_write_end(r10bio->mddev);
>>>    1536				bio_endio(r10bio->master_bio);
>>>    1537				free_r10bio(r10bio);
>>>    1538				break;
>>>    1539			}
>>>    1540		}
>>>    1541	}
>>>    1542	
>>>
>>> ---
>>> 0-DAY CI Kernel Test Service, Intel Corporation
>>> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
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