Messages in this thread | | | Date | Wed, 31 Jul 2013 07:13:06 -0700 | From | "Paul E. McKenney" <> | Subject | Re: ipv4: crash at leaf_walk_rcu |
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On Wed, Jul 31, 2013 at 03:13:23PM +0200, Hannes Frederic Sowa 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().
Even better! ;-)
Thanx, Paul
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