Re: [PATCH] ipv4: fix the rcu race between free_fib_info andip_route_output_slow

[Eric Dumazet]

On Tue, 2012-05-22 at 23:23 -0400, David Miller wrote:
> From: Yanmin Zhang <yanmin_zhang@xxxxxxxxxxxxxxx>
> 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).
> --

Its more than that I'm afraid.

fi->fib_dev (aka fib_nh[0].nh_dev) need full RCU protection.

Also the "fib_info_cnt--;" must stay in free_fib_info() (so that it is
protected by RTNL)



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/