Subject: Re: [syzbot] [block?] WARNING in blkdev_put (2)
To:     Julian Ruess <julianr@linux.ibm.com>,
        Alexander Egorenkov <egorenar@linux.ibm.com>,
        syzbot+2bcc0d79e548c4f62a59@syzkaller.appspotmail.com
Cc:     axboe@kernel.dk, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        jack@suse.cz, hch@lst.de, Niklas Schnelle <schnelle@linux.ibm.com>,
        Gerd Bayer <gbayer@linux.ibm.com>,
        "yukuai (C)" <yukuai3@huawei.com>
References: <87lekfne28.fsf@oc8242746057.ibm.com>
 <f9649d501bc8c3444769418f6c26263555d9d3be.camel@linux.ibm.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <26079e08-857d-6216-0921-bdef369f3316@huaweicloud.com>
Date:   Tue, 7 Mar 2023 09:42:18 +0800
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Hi,

在 2023/03/06 23:00, Julian Ruess 写道:
> On Thu, 2023-03-02 at 20:33 +0100, Alexander Egorenkov wrote:
>>
>> Hi,
>>
>> we are seeing a similar problem on s390x architecture when
>> partitioning
>> a NVMe disk on linux-next.
>>
>>
>>    [   70.403015]  nvme0n1: p1
>>    [   70.403197] ------------[ cut here ]------------
>>    [   70.403199] WARNING: CPU: 8 PID: 2452 at block/bdev.c:845
>> blkdev_put+0x280/0x298
> 
> ...
> 
>> The problem appeared about a week ago.
>>
>> Regards
>> Alex
> 
> Hi all,
> 
> I bisected this to:
> 
> commit e5cfefa97bccf956ea0bb6464c1f6c84fd7a8d9f
> Author: Yu Kuai <yukuai3@huawei.com>
> Date:   Fri Feb 17 10:22:00 2023 +0800
>                                                                                        
>      block: fix scan partition for exclusively open device again

Yes, thanks for the report, I figure out that I made a mistake here.

Following patch should fix this problem:

diff --git a/block/genhd.c b/block/genhd.c
index 3ee5577e1586..02d9cfb9e077 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -385,7 +385,7 @@ int disk_scan_partitions(struct gendisk *disk, 
fmode_t mode)
         if (IS_ERR(bdev))
                 ret =  PTR_ERR(bdev);
         else
-               blkdev_put(bdev, mode);
+               blkdev_put(bdev, mode & ~FMODE_EXCL);

Thanks,
Kuai
>                                                                                        
>      As explained in commit 36369f46e917 ("block: Do not reread
> partition table
>      on exclusively open device"), reread partition on the device that
> is
>      exclusively opened by someone else is problematic.
>                                                                                        
>      This patch will make sure partition scan will only be proceed if
> current
>      thread open the device exclusively, or the device is not opened
>      exclusively, and in the later case, other scanners and exclusive
> openers
>      will be blocked temporarily until partition scan is done.
>                                                                                        
>      Fixes: 10c70d95c0f2 ("block: remove the bd_openers checks in
> blk_drop_partitions")
>      Cc: <stable@vger.kernel.org>
>      Suggested-by: Jan Kara <jack@suse.cz>
>      Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>      Reviewed-by: Christoph Hellwig <hch@lst.de>
>      Link:
> https://lore.kernel.org/r/20230217022200.3092987-3-yukuai1@huaweicloud.com
>   
>      Signed-off-by: Jens Axboe <axboe@kernel.dk>
> 
> 
> 
> Regards
> Julian
>