Re: [PATCH] scsi/sg: don't grab scsi host module reference

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

Hi,

在 2023/07/05 1:04, Marc Hartmayer 写道:
> On Thu, Jun 22, 2023 at 12:01 AM +0800, Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > Link: https://lore.kernel.org/all/1760da91-876d-fc9c-ab51-999a6f66ad50@xxxxxxxxxx/
> > Fixes: db59133e9279 ("scsi: sg: fix blktrace debugfs entries leakage")
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > ---
> >   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
> .