netdev - Re: [PATCH] net: sk == 0xffffffff fix

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Message-ID: <1386685557.30495.344.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 10 Dec 2013 06:25:57 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andrzej Pietrasiewicz <andrzej.p@...sung.com>
Cc:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: sk == 0xffffffff fix - not for commit

On Tue, 2013-12-10 at 07:55 +0100, Andrzej Pietrasiewicz wrote:
> W dniu 09.12.2013 16:31, Eric Dumazet pisze:
> > On Mon, 2013-12-09 at 12:47 +0100, Andrzej Pietrasiewicz wrote:
> >> NOT FOR COMMITTING TO MAINLINE.
> >>
> >> With g_ether loaded the sk occasionally becomes 0xffffffff.
> >> It happens usually after transferring few hundreds of kilobytes to few
> >> tens of megabytes. If sk is 0xffffffff then dereferencing it causes
> >> kernel panic.
> >>
> >> This is a *workaround*. I don't know enough net code to understand the core
> >> of the problem. However, with this patch applied the problems are gone,
> >> or at least pushed farther away.
> >
> > Is it happening on SMP or UP ?
> 
> UP build, S5PC110

OK

I believe you need additional debugging to track the exact moment
0xffffffff is fed to 'sk'

It looks like a very strange bug, involving a problem in some assembly
helper, register save/restore, compiler bug or stack corruption or
something.

You should not have more than 150 instructions to decode, including
__inet_lookup_established()

Since __inet_lookup_established() dereferences the socket pointer, I do
not see why it would crash ~20 instructions _later_



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