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SubjectRe: [PATCH] scsi/sg: don't grab scsi host module reference
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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
> .
>

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