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

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Message-ID: <CAD1RLj1SJBPg0F4Dyu_EL05FVm9c7ZZj7_=oRPAdQU4BDUwu5g@mail.gmail.com>
Date:	Wed, 19 Oct 2011 02:46:26 +0530
From:	Ankit Jain <mail@...itjain.org>
To:	Jack Wang <jack_wang@...sh.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	Alan Stern <stern@...land.harvard.edu>,
	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 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?

-Ankit
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