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Subject: Re: [PATCH] scsi/sg: don't grab scsi host module reference
To:     Marc Hartmayer <mhartmay@linux.ibm.com>,
        Yu Kuai <yukuai1@huaweicloud.com>
Cc:     linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, yangerkun@huawei.com, hch@lst.de,
        chaitanyak@nvidia.com, shinichiro.kawasaki@wdc.com,
        dgilbert@interlog.com, jejb@linux.ibm.com,
        martin.petersen@oracle.com, axboe@kernel.dk,
        Benjamin Block <bblock@linux.ibm.com>,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20230621160111.1433521-1-yukuai1@huaweicloud.com>
 <87lefv622n.fsf@linux.ibm.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <70432d91-3909-ac3c-9c36-5f7484c1fdf1@huaweicloud.com>
Date:   Wed, 5 Jul 2023 09:43:53 +0800
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Hi,

在 2023/07/05 1:04, Marc Hartmayer 写道:
> On Thu, Jun 22, 2023 at 12:01 AM +0800, Yu Kuai <yukuai1@huaweicloud.com> wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> In order to prevent request_queue to be freed before cleaning up
>> blktrace debugfs entries, commit db59133e9279 ("scsi: sg: fix blktrace
>> debugfs entries leakage") use scsi_device_get(), however,
>> scsi_device_get() will also grab scsi module reference and scsi module
>> can't be removed.
>>
>> It's reported that blktests can't unload scsi_debug after block/001:
>>
>> blktests (master) # ./check block
>> block/001 (stress device hotplugging) [failed]
>>       +++ /root/blktests/results/nodev/block/001.out.bad 2023-06-19
>>        Running block/001
>>        Stressing sd
>>       +modprobe: FATAL: Module scsi_debug is in use.
>>
>> Fix this problem by grabbing request_queue reference directly, so that
>> scsi host module can still be unloaded while request_queue will be
>> pinged by sg device.
>>
>> Reported-by: Chaitanya Kulkarni <chaitanyak@nvidia.com>
>> Link: https://lore.kernel.org/all/1760da91-876d-fc9c-ab51-999a6f66ad50@nvidia.com/
>> Fixes: db59133e9279 ("scsi: sg: fix blktrace debugfs entries leakage")
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   drivers/scsi/sg.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
>> index 2433eeef042a..dcb73787c29d 100644
>> --- a/drivers/scsi/sg.c
>> +++ b/drivers/scsi/sg.c
>> @@ -1497,7 +1497,7 @@ sg_add_device(struct device *cl_dev)
>>   	int error;
>>   	unsigned long iflags;
>>   
>> -	error = scsi_device_get(scsidp);
>> +	error = blk_get_queue(scsidp->request_queue);
>>   	if (error)
>>   		return error;
>>   
>> @@ -1558,7 +1558,7 @@ sg_add_device(struct device *cl_dev)
>>   out:
>>   	if (cdev)
>>   		cdev_del(cdev);
>> -	scsi_device_put(scsidp);
>> +	blk_put_queue(scsidp->request_queue);
>>   	return error;
>>   }
>>   
>> @@ -1575,7 +1575,7 @@ sg_device_destroy(struct kref *kref)
>>   	 */
>>   
>>   	blk_trace_remove(q);
>> -	scsi_device_put(sdp->device);
>> +	blk_put_queue(q);
>>   
>>   	write_lock_irqsave(&sg_index_lock, flags);
>>   	idr_remove(&sg_index_idr, sdp->index);
>> -- 
>> 2.39.2
> 
> Hi,
> 
> This change (bisected) triggers a regression in our KVM on s390x CI. The
> symptom is that a “scsi_debug device” does not bind to the scsi_generic
> driver. On s390x you can reproduce the problem as follows (I have not
> tested on x86):
> 
> With this patch applied:
> 
> $ sudo modprobe scsi_debug
> $ # Get the 'scsi_host,channel,target_number,LUN' tuple for the scsi_debug device
> $ lsscsi |grep scsi_debug |awk '{ print $1 }'
> [0:0:0:0]
> $ sudo stat /sys/bus/scsi/devices/0:0:0:0/scsi_generic
> stat: cannot statx '/sys/bus/scsi/devices/0:0:0:0/scsi_generic': No such file or directory
> 
> 
> Patch reverted:
> 

I didn't figure out the root cause, howver, have you tried to reviert
this patch as well?

db59133e9279 ("scsi: sg: fix blktrace debugfs entries leakage"

Thanks,
Kuai
> $ sudo modprobe scsi_debug
> $ lsscsi |grep scsi_debug |awk '{ print $1 }'
> [0:0:0:0]
> $ sudo stat /sys/bus/scsi/devices/0:0:0:0/scsi_generic
>    File: /sys/bus/scsi/devices/0:0:0:0/scsi_generic
>    Size: 0         	Blocks: 0          IO Block: 4096   directory
> Device: 0,20	Inode: 12155       Links: 3
> …
> 
> Any ideas?
> 
>   Marc
> .
>