linux-kernel - Re: next-20081119: general protection fault: get_next_timer

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Date:	Tue, 25 Nov 2008 09:51:09 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	malahal@...ibm.com
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Anderson <andmike@...ux.vnet.ibm.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Alexander Beregalov <a.beregalov@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-next@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, linux-scsi@...r.kernel.org,
	David Miller <davem@...emloft.net>
Subject: Re: next-20081119: general protection fault: get_next_timer_interrupt()

On Mon, Nov 24 2008, malahal@...ibm.com wrote:
> Stephen Rothwell [sfr@...b.auug.org.au] wrote:
> > > The block timer code calls del_timer(), should it call del_timer_sync()?
> > > It is possible although unlikely that you are hitting del_timer_sync vs
> > > del_timer problem in the block timeout code. Can only be seen on SMP
> > > systems though!
> > 
> > Is this still a problem in next-20081121? In that tree, the block commit
> > "block: leave the request timeout timer running even on an empty list"
> > was changed to add this:
> > 
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index 04267d6..44f547c 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -391,6 +391,7 @@ EXPORT_SYMBOL(blk_stop_queue);
> >  void blk_sync_queue(struct request_queue *q)
> >  {
> >  	del_timer_sync(&q->unplug_timer);
> > +	del_timer_sync(&q->timeout);
> >  	kblockd_flush_work(&q->unplug_work);
> >  }
> >  EXPORT_SYMBOL(blk_sync_queue);
> 
> I was looking at the Linux tree. Clearly same problem doesn't exist with
> the above commit! I wonder why kblockd_flush_work() is called after the
> del_timer_sync(). It makes sense to cancel the work and then shutdown
> the timer(s). I doubt if you are running into this problem though.

If the kernel tested doesn't include the above fix, it'll surely go
boom. Can someone verify that this is the case?

-- 
Jens Axboe

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