Message-ID: <1337757862.14538.199.camel@ymzhang.sh.intel.com>
Subject: Re: [PATCH] ipv4: fix the rcu race between free_fib_info and
 ip_route_output_slow
From: Yanmin Zhang <yanmin_zhang@linux.intel.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David Miller <davem@davemloft.net>, kunx.jiang@intel.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Date: Wed, 23 May 2012 15:24:22 +0800
In-Reply-To: <1337757238.3361.1965.camel@edumazet-glaptop>
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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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