linux-kernel - Re: [1/2] [NET] link_watch: Move link watch list into net

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Message-Id: <20070510151426.d808384f.akpm@linux-foundation.org>
Date:	Thu, 10 May 2007 15:14:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Christoph Hellwig <hch@...radead.org>, Andi Kleen <ak@...e.de>,
	virtualization@...ts.osdl.org, lkml <linux-kernel@...r.kernel.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Ian Pratt <ian.pratt@...source.com>,
	Christian Limpach <Christian.Limpach@...cam.ac.uk>,
	netdev@...r.kernel.org, Jeff Garzik <jeff@...zik.org>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>, Valdis.Kletnieks@...edu
Subject: Re: [1/2] [NET] link_watch: Move link watch list into net_device

On Thu, 10 May 2007 15:00:05 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Herbert Xu wrote:
> > [NET] link_watch: Move link watch list into net_device
> >
> > These days the link watch mechanism is an integral part of the
> > network subsystem as it manages the carrier status.  So it now
> > makes sense to allocate some memory for it in net_device rather
> > than allocating it on demand.
> 
> I think there's a problem with one of these two patches.  I've been
> noticing that one of my events/X threads has been going into a spin for
> about 5 mins after boot.  I added some debugging to
> kernel/workqueue.c:run_workqueue, since its that loop which seems to be
> spinning due to list corruption.
> 
> When I look to see if that loop has iterated for more than 100 times in
> one go (which seems unlikely),  I get this:
> 
> BUG: cpu 3, count=101 list screwup on c04babe4, func c03217e8
> func=linkwatch_event+0x0/0x2a
>  [<c0109173>] show_trace_log_lvl+0x1a/0x30
>  [<c0109c7f>] show_trace+0x12/0x14
>  [<c0109d0c>] dump_stack+0x16/0x18
>  [<c0137c25>] run_workqueue+0x97/0x18c
>  [<c01386a4>] worker_thread+0xe5/0xf5
>  [<c013afe9>] kthread+0x3b/0x62
>  [<c0108d47>] kernel_thread_helper+0x7/0x10
>  =======================
> 
> 
> I wonder if the problem is that the linkwatch_work is being rescheduled
> when its already been scheduled, or something like that?

Five minutes after boot is when jiffies wraps.  Are you sure it's
a list-screwup rather than a jiffy-wrap screwup?
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