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

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Message-ID: <20081125020852.GA27280@us.ibm.com>
Date:	Mon, 24 Nov 2008 18:08:52 -0800
From:	malahal@...ibm.com
To:	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	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>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: next-20081119: general protection fault:
	get_next_timer_interrupt()

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.

-Malahal.
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