linux-kernel - Re: Linux 3.0 oopses when pulling a USB CDROM

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Date:	Tue, 18 Oct 2011 16:30:25 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Ankit Jain <mail@...itjain.org>
Cc:	Jack Wang <jack_wang@...sh.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Andi Kleen <andi@...stfloor.org>, axboe@...nel.dk,
	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 Wed, 2011-10-19 at 02:46 +0530, Ankit Jain wrote:
> On Wed, Jul 20, 2011 at 3:28 PM, Jack Wang <jack_wang@...sh.com> wrote:
> >>
> <snip>
> >> 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.
> 
> I don't see this patch in scsi-misc-2.6 or linus' tree. Is there a
> different patch that fixes the
> issue?

It should be fixed by

commit 777eb1bf15b8532c396821774bf6451e563438f5
Author: Hannes Reinecke <hare@...e.de>
Date:   Wed Sep 28 08:07:01 2011 -0600

    block: Free queue resources at blk_release_queue()

James


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