linux-kernel - Re: [Bug 25832] kernel crashes when a mounted ext3/4 file system is physically removed

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Date:	Thu, 22 Sep 2011 13:20:47 -0300
From:	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Rocko Requin <rockorequin@...mail.com>,
	Hannes Reinecke <hare@...e.de>,
	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>,
	Ben Hutchings <ben@...adent.org.uk>, jaxboe@...ionio.com,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	tytso@....edu,
	Kernel development list <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [Bug 25832] kernel crashes when a mounted ext3/4 file system is
 physically removed

On Thu, Sep 22, 2011 at 11:16:30AM -0400, Alan Stern wrote:
> Rocko:
> 
> Can you try testing this patch instead of all the patches I sent to 
> you (but keep Ted's patch)?
> 
> Alan Stern
> 
> On Thu, 22 Sep 2011, Hannes Reinecke wrote:
> 
> > On 09/20/2011 09:32 AM, Jun'ichi Nomura wrote:
> > > On 09/19/11 08:00, Ben Hutchings wrote:
> > [ .. ]
> > >>
> > >> There have been reports of this in Debian going back to 2.6.39:
> > >>
> > >> http://bugs.debian.org/631187
> > >> http://bugs.debian.org/636263
> > >> http://bugs.debian.org/642043
> > >>
> > >> Plus possibly related crashes in elv_put_request after CD-ROM removal:
> > >>
> > >> http://bugs.debian.org/633890
> > >> http://bugs.debian.org/634681
> > >> http://bugs.debian.org/636103
> > >>
> > >> The former was also reported in Ubuntu since their 2.6.38-10:
> > >>
> > >> https://bugs.launchpad.net/debian/+source/linux-2.6/+bug/793796
> > >>
> > >> The result of the discussion there was that it appeared to be a
> > >> regression due to commit 86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b 
> > >> ("[SCSI] put stricter guards on queue dead checks") which was also
> > >> included in a stable update for 2.6.38.
> > >>
> > >> There was also a report on bugzilla.kernel.org, though no-one can see
> > >> quite what that says now:
> > >>
> > >> https://bugzilla.kernel.org/show_bug.cgi?id=38842
> > >>
> > >> I also reported most of the above to James Bottomley and linux-scsi
> > >> nearly 2 months ago, to no response.
> > > 
> > > I've reported a similar oops related to the above commit:
> > >   [BUG] Oops when SCSI device under multipath is removed
> > >   https://lkml.org/lkml/2011/8/10/11
> > > 
> > > Elevator being removed is the core of the problem.
> > > And the essential issue seems 2 different models of queue/driver relation
> > > implied by queue_lock.
> > > 
> > > If reverting the commit is not an option,
> > > until somebody comes up to fix the essential issue,
> > > the patch below should close the regressions introduced by the commit.
> > > 
> > Why do you have to do it that complicated?
> > Couldn't we just state that any external lock is being disconnected from
> > queue_lock after blk_cleanup_queue()?
> > 
> > Then something like this should suffice here:
> 
> 
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 90e1ffd..a4ac005 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -367,10 +367,8 @@ void blk_cleanup_queue(struct request_queue *q)
>         queue_flag_set_unlocked(QUEUE_FLAG_DEAD, q);
>         mutex_unlock(&q->sysfs_lock);
> 
> -       if (q->elevator)
> -               elevator_exit(q->elevator);
> -
> -       blk_throtl_exit(q);
> +       if (q->queue_lock != q->__queue_lock)
> +               q->queue_lock = q->__queue_lock;

That should be &q->__queue_lock.

Regards,
Cascardo.

> 
>         blk_put_queue(q);
>  }
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 0ee17b5..a5a756b 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -477,6 +477,11 @@ static void blk_release_queue(struct kobject *kobj)
> 
>         blk_sync_queue(q);
> 
> +       if (q->elevator)
> +               elevator_exit(q->elevator);
> +
> +       blk_throtl_exit(q);
> +
>         if (rl->rq_pool)
>                 mempool_destroy(rl->rq_pool);
> 
> 
> > And yeah, I find it pretty annoying, too.
> > 
> > Cheers,
> > 
> > Hannes
> > 
> 
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