netdev - Re: [PATCH for stable 3.10] xen-netback: drop SKB from internal queue if frontend is disconnected

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Message-ID: <1405084529.27875.1.camel@kazak.uk.xensource.com>
Date:	Fri, 11 Jul 2014 14:15:29 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	<xen-devel@...ts.xen.org>, <netdev@...r.kernel.org>,
	Philipp Hahn <hahn@...vention.de>
Subject: Re: [PATCH for stable 3.10] xen-netback: drop SKB from internal
 queue if frontend is disconnected

On Fri, 2014-07-11 at 14:08 +0100, Wei Liu wrote:
> In 88a810def7 ("xen-netback: fix refcnt unbalance for 3.10"), we moved
> the ref counting code from xenvif_disconnect to xenvif_free.

Since this was a 3.10 specific backport that explains why this is also
such?

> It can occur that frontend is disconnected while there's still SKB
> stuck in netback's rx_queue in rare case. When netback thread wakes up,
> it will try to write to an already unmapped ring, resulting in kernel
> oops.
> 
> Moving the ref counting back to xenvif_disconnect isn't an option as it
> reintroduces an old bug. Further more, writing into a dead frontend's
> ring and memory is just wrong. Dropping those SKBs seems to be a good
> strategy.
> 
> This patch fixes that corner case: introduce a flag to indicate whether
> frontend ring is mapped. If the ring is unmapped, just drop those SKBs.
> 
> This bug only manifests in 3.10 kernel. Kernel >=3.12 doesn't have it.

What about 3.11?


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