linux-kernel - Re: [PATCH] ipv4: fix the rcu race between free_fib_info and ip_route_output

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Message-ID: <1337743841.14538.178.camel@ymzhang.sh.intel.com>
Date:	Wed, 23 May 2012 11:30:41 +0800
From:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
To:	David Miller <davem@...emloft.net>
Cc:	kunx.jiang@...el.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv4: fix the rcu race between free_fib_info and
 ip_route_output_slow

On Tue, 2012-05-22 at 23:23 -0400, David Miller wrote:
> From: Yanmin Zhang <yanmin_zhang@...ux.intel.com>
> Date: Wed, 23 May 2012 11:02:03 +0800
> 
> > 1) Why does free_fib_info call call_rcu instead of releasing fi directly?
> > I assume other cpu might be accessing it. nexthop_nh->nh_dev is in fi.
> > If other cpu are accessing it, here resetting to NULL would cause other
> > cpu panic.
> 
> Because fib trie lookups are done with RCU locking, therefore we must
> use RCU freeing to release the object.
> 
> What I was trying to impart to you is that removing the NULL
> assignment is wrong and that an alternative fix is warranted (hint:
> consider moving something into the RCU release).
Thanks for the explanation.

How about the new patch posted in the end of previous reply? It does move the
the resetting to RCU release.
https://lkml.org/lkml/2012/5/22/558?

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