netdev - Re: locking api self-test hanging

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Message-Id: <20080206011643.d9021649.akpm@linux-foundation.org>
Date:	Wed, 6 Feb 2008 01:16:43 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	netdev@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	Stephen Hemminger <shemminger@...ux-foundation.org>
Subject: Re: locking api self-test hanging

On Wed, 6 Feb 2008 00:34:12 -0800 Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 4 Feb 2008 04:43:04 -0800 Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Sun, 3 Feb 2008 15:07:44 -0800 Andrew Morton <akpm@...ux-foundation.org> wrote:
> > 
> > > On Sun, 3 Feb 2008 15:02:46 -0800 Andrew Morton <akpm@...ux-foundation.org> wrote:
> > > 
> > > > 
> > > > With current mainline I'm getting intermittent hangs here:
> > > > 
> > > > 	http://userweb.kernel.org/~akpm/p2033590.jpg
> > > > 
> > > > with this config:
> > > > 
> > > > 	http://userweb.kernel.org/~akpm/config-sony.txt
> > > > 
> > > > on the Vaio.  Sometimes it boots (then hits another different hang),
> > > > sometimes it gets stuck there.
> > 
> > CONFIG_DEBUG_LOCKING_API_SELFTESTS=n fixed that up.
> > 
> > > 
> > > The second hang is in kobject_uevent_init().  All that function does is call
> > > netlink_kernel_create().
> > 
> > And I've fully bisected this hang twice and both times came up with
> > 
> > commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
> > Author: Stephen Hemminger <shemminger@...ux-foundation.org>
> > Date:   Mon Nov 19 19:24:52 2007 -0800
> > 
> >     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
> > 
> > which is stupid because that patch doesn't do anything.
> > 
> > However I am using netconsole-over-e100 and the hang does go away when I
> > disable netconsole on the kernel boot command line.
> > 
> > I'd say it's some timing thing in netpoll/netconsole/napi/etc.
> > 
> 
> I'm seeing this netconsole hang on a second machine now.  Current
> mainline.  It also has e100.  This one is SMP ancient PIII.
> 
> Config: http://userweb.kernel.org/~akpm/config-vmm.txt
> 

I can reproduce this on a third machine: the t61p laptop: dual x86_64 with
e1000.

It seems to need quite a lot of printk activity to make it happen.  Turning
on initcall_debug is a suitable way of triggering it.

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