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.

[Xiao Ni <xni@redhat.com>]

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

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