Re: [PATCH-next v2 2/2] scsi: fix iscsi rescan fails to create block device

[Yu Kuai]

Hi,

在 2023/01/29 14:46, Greg KH 写道:
> On Sun, Jan 29, 2023 at 09:13:55AM +0800, Yu Kuai wrote:
> > Hi, Greg
> >
> > 在 2023/01/28 18:45, Greg KH 写道:
> > > > diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> > > > index cac7c902cf70..a22109cdb8ef 100644
> > > > --- a/drivers/scsi/scsi_sysfs.c
> > > > +++ b/drivers/scsi/scsi_sysfs.c
> > > > @@ -1535,9 +1535,7 @@ static void __scsi_remove_target(struct scsi_target *starget)
> > > >    		if (sdev->channel != starget->channel ||
> > > >    		    sdev->id != starget->id)
> > > >    			continue;
> > > > -		if (sdev->sdev_state == SDEV_DEL ||
> > > > -		    sdev->sdev_state == SDEV_CANCEL ||
> > > > -		    !get_device(&sdev->sdev_gendev))
> > > > +		if (!get_device_unless_zero(&sdev->sdev_gendev))
> > >
> > > If sdev_gendev is 0 here, the object is gone and you are working with
> > > memory that is already freed so something is _VERY_ wrong.
> >
> > In fact, this patch will work:
> >
> > In __scsi_remove_target(), 'host_lock' is held to protect iterating
> > siblings, and object will wait for this lock in
> > scsi_device_dev_release() to remove siblings. Hence sdev will not be
> > freed untill the lock is released.
>
> Then you got lucky, as that is not how a reference counted object should
> be working (i.e. the reference dropped to 0 and it still be kept alive.)
>
> Please fix up the scsi logic here, don't abuse the reference count code.

Thanks for the reply, I agree that we should fix this in scsi layer.

Kuai