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

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Date:	Wed, 23 May 2012 15:24:22 +0800
From:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, 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 Wed, 2012-05-23 at 09:13 +0200, Eric Dumazet wrote:
> On Wed, 2012-05-23 at 08:55 +0200, Eric Dumazet wrote:
> 
> > Please hold on, I'll send a v2
> 
> I believe your patch should be fine, if you move back the
> fib_info_cnt--;
> 
> So only do the dev_put() in free_fib_info_rcu().
We would do so in a new patch.

> 
> No need to clear nh_dev to NULL since we are freeing fi at the end of
> function.
David suggests to reset it to NULL to detect other potential
race conditions.

Besides above suggestions, how do you think about:

fib_create_info=>fib_find_info, but fib_find_info is not protected by
fib_info_lock. See the codes:

fib_create_info()
{
	...
link_it:
        ofi = fib_find_info(fi);
        if (ofi) {
                fi->fib_dead = 1;
                free_fib_info(fi);
                ofi->fib_treeref++;
                return ofi;
        }
        fi->fib_treeref++;
        atomic_inc(&fi->fib_clntref);
        spin_lock_bh(&fib_info_lock);

	...
}

I plan to change it to hold fib_info_lock before calling fib_find_info. Is
it ok for you?

Thanks for the direct speaking.

Yanmin


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