linux-kernel - Re: [PATCH] block: tolerate 0 byte discard_granularity in __blkdev_issue

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Message-ID: <SN4PR0401MB35983A30C6AE9886EF6E91C79B4A0@SN4PR0401MB3598.namprd04.prod.outlook.com>
Date:   Tue, 4 Aug 2020 14:37:50 +0000
From:   Johannes Thumshirn <Johannes.Thumshirn@....com>
To:     Coly Li <colyli@...e.de>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>
CC:     "linux-bcache@...r.kernel.org" <linux-bcache@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ming Lei <ming.lei@...hat.com>,
        Hannes Reinecke <hare@...e.com>, Xiao Ni <xni@...hat.com>,
        Bart Van Assche <bvanassche@....org>,
        Christoph Hellwig <hch@....de>,
        Enzo Matsumiya <ematsumiya@...e.com>,
        Jens Axboe <axboe@...nel.dk>, Evan Green <evgreen@...omium.org>
Subject: Re: [PATCH] block: tolerate 0 byte discard_granularity in
 __blkdev_issue_discard()

On 04/08/2020 16:34, Coly Li wrote:
> On 2020/8/4 22:31, Johannes Thumshirn wrote:
>> On 04/08/2020 16:23, Coly Li wrote:
>>> This is the procedure to reproduce the panic,
>>>   # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
>>>   # losetup -f /dev/nvme0n1 --direct-io=on
>>>   # blkdiscard /dev/loop0 -o 0 -l 0x200
>>
>> losetup -f /dev/sdX isn't it?
>>
> 
> In my case, I use a NVMe SSD as the backing device of the loop device.
> Because I don't have a scsi lun.
> 
> And loading scsi_debug module seems necessary, otherwise the discard
> process just hang and I cannot see the kernel panic (I don't know why yet).

OK, now that's highly interesting. Does it also happen if you back loop with
a file? loop_config_discard() has different cases for the different backing devices/files. S