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Date: Wed, 31 Jul 2013 19:01:26 +0530
Message-ID: <CAOaiJ-mNeR63cOGBxUOJTP40mzS1QMzNNAhc+BbFAoE1NQc30A@mail.gmail.com>
Subject: Re: ipv4: crash at leaf_walk_rcu
From: vinayak menon <vinayakm.list@gmail.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        vinayak menon <vinayakm.list@gmail.com>, linux-kernel@vger.kernel.org,
        davem@davemloft.net, getarunks@gmail.com, netdev@vger.kernel.org
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On Wed, Jul 31, 2013 at 6:43 PM, Hannes Frederic Sowa
<hannes@stressinduktion.org> wrote:
> On Wed, Jul 31, 2013 at 05:55:13AM -0700, Paul E. McKenney wrote:
>> On Wed, Jul 31, 2013 at 04:40:47PM +0530, vinayak menon wrote:
>> > Hi,
>> >
>> > A crash was seen on 3.4.5 kernel during some random wlan operations.
>> >
>> > CPU: Single core ARM Cortex A9.
>> >
>> > fib_route_seq_next was called with second argument (void *v) as 0xd6e3e360
>> > which is a "freed" object of the "ip_fib_trie" cache. I confirmed that the
>> > object was freed with crash utility.
>> >
>> > Sequence: fib_route_seq_next->trie_nextleaf->leaf_walk_rcu
>> >
>> > As "v" was a freed object, inside trie_nextleaf(), node_parent_rcu()
>> > returned an invalid tnode. But as I had enabled slab poisoning and the
>> > object was already freed, the tnode was 0x6b6b6b6b. And this was passed to
>> > leaf_walk_rcu and resulted in the crash.
>> >
>> > fib_route_seq_start, takes rcu_read_lock(), but free_leaf
>> > calls call_rcu_bh. Can this be the problem ?
>> > Should rcu_read_lock() in fib_route_seq_start be changed to rcu_read_lock_bh()
>> > ?
>>
>> One way or the other, the RCU read-side primitives need to match the RCU
>> update-side primitives.  Adding netdev...
>
> Already fixed by:
>
> commit 0c03eca3d995e73d691edea8c787e25929ec156d
> Author: Eric Dumazet <edumazet@google.com>
> Date:   Tue Aug 7 00:47:11 2012 +0000
>
>     net: fib: fix incorrect call_rcu_bh()
>
>     After IP route cache removal, I believe rcu_bh() has very little use and
>     we should remove this RCU variant, since it adds some cycles in fast
>     path.
>
>     Anyway, the call_rcu_bh() use in fib_true is obviously wrong, since
>     some users only assert rcu_read_lock().
>

Thanks. I missed this somehow.
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