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Date:	Wed, 20 Jul 2011 17:58:01 +0800
From:	"Jack Wang" <jack_wang@...sh.com>
To:	"'Dan Williams'" <dan.j.williams@...el.com>,
	"'Alan Stern'" <stern@...land.harvard.edu>
Cc:	"'Andi Kleen'" <andi@...stfloor.org>, <axboe@...nel.dk>,
	"'James Bottomley'" <James.Bottomley@...senpartnership.com>,
	"'Dave Jones'" <davej@...hat.com>,
	"'SCSI development list'" <linux-scsi@...r.kernel.org>,
	"'Kernel development list'" <linux-kernel@...r.kernel.org>,
	"'Rafael J. Wysocki'" <rjw@...k.pl>,
	"'USB list'" <linux-usb@...r.kernel.org>
Subject: RE: Linux 3.0 oopses when pulling a USB CDROM

> 
> On Sat, Jul 2, 2011 at 12:59 PM, Alan Stern <stern@...land.harvard.edu>
wrote:
> > On Sat, 2 Jul 2011, Andi Kleen wrote:
> >
> >> > The problem is that blk_peek_request() calls scsi_prep_fn(), which
> >> > does this:
> >> >
> >> >     struct scsi_device *sdev = q->queuedata;
> >> >     int ret = BLKPREP_KILL;
> >> >
> >> >     if (req->cmd_type == REQ_TYPE_BLOCK_PC)
> >> >             ret = scsi_setup_blk_pc_cmnd(sdev, req);
> >> >     return scsi_prep_return(q, req, ret);
> >> >
> >> > It doesn't check to see if sdev is NULL, nor does
> >> > scsi_setup_blk_pc_cmnd().  That accounts for this error:
> >>
> >> I actually added a NULL check in scsi_setup_blk_pc_cmnd early on,
> >> but that just caused RCU CPU stalls afterwards and then eventually
> >> a hung system.
> >
> > The RCU problem is likely to be a separate issue.  It might even be a
> > result of the use-after-free problem with the elevator.
> >
> > At any rate, it's clear that the crash in the refcounting log you
> > posted occurred because scsi_setup_blk_pc_cmnd() called
> > scsi_prep_state_check(), which tried to dereference the NULL pointer.
> >
> > Would you like to try this patch to see if it fixes the problem?  As I
> > said before, I'm not certain it's the best thing to do, but it worked
> > on my system.
> >
> > Alan Stern
> >
> >
> >
> >
> > Index: usb-3.0/drivers/scsi/scsi_lib.c
> > ===================================================================
> > --- usb-3.0.orig/drivers/scsi/scsi_lib.c
> > +++ usb-3.0/drivers/scsi/scsi_lib.c
> > @@ -1247,6 +1247,8 @@ int scsi_prep_fn(struct request_queue *q
> >        struct scsi_device *sdev = q->queuedata;
> >        int ret = BLKPREP_KILL;
> >
> > +       if (!sdev)
> > +               return ret;
> >        if (req->cmd_type == REQ_TYPE_BLOCK_PC)
> >                ret = scsi_setup_blk_pc_cmnd(sdev, req);
> >        return scsi_prep_return(q, req, ret);
> > Index: usb-3.0/drivers/scsi/scsi_sysfs.c
> > ===================================================================
> > --- usb-3.0.orig/drivers/scsi/scsi_sysfs.c
> > +++ usb-3.0/drivers/scsi/scsi_sysfs.c
> > @@ -322,6 +322,8 @@ static void scsi_device_dev_release_user
> >                kfree(evt);
> >        }
> >
> > +       /* Freeing the queue signals to block that we're done */
> > +       scsi_free_queue(sdev->request_queue);
> >        blk_put_queue(sdev->request_queue);
> >        /* NULL queue means the device can't be used */
> >        sdev->request_queue = NULL;
> > @@ -936,8 +938,6 @@ void __scsi_remove_device(struct scsi_de
> >        /* cause the request function to reject all I/O requests */
> >        sdev->request_queue->queuedata = NULL;
> >
> > -       /* Freeing the queue signals to block that we're done */
> > -       scsi_free_queue(sdev->request_queue);
> >        put_device(dev);
> >  }
> 
> This patch seems to resolve the block/scsi null-ptr de-references in
> our libsas/isci environment, we have yet to try James' alternative
> [1].  Do we potentially need both?
> 
> Commit 86cbfb56 moved scsi_free_queue to __scsi_remove_device() but it
> seems only the "sdev->request_queue->queuedata = NULL" needed to be
> moved?
> 
> The conversation appeared to be awaiting test results...
> 
> [1]: http://marc.info/?l=linux-scsi&m=131007155700831&w=2
> 
> --
> Dan
[Jack Wang] 
This patch fix kernel panic issue when hot-plut disk during I/O, I test it
using pm8001 with 3.0.0-rc6 with above patch.


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