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...
Thanx, Paul
> ----------------------------------------------------------------------------
> PC is at leaf_walk_rcu+0x10/0xa0
> LR is at fib_route_seq_next+0x58/0x74
> pc : [<c0500e5c>] lr : [<c050108c>] psr: a0000013
> sp : c150bee0 ip : 00000000 fp : 00000000
> r10: 00000400 r9 : 53701020 r8 : c32345c0
> r7 : 00000000 r6 : 00000001 r5 : 00000000 r4 : 00000002
> r3 : 6b6b6b6b r2 : 00000001 r1 : d6e3e360 r0 : 6b6b6b6a
> Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
> Control: 10c53c7d Table: 835dc059 DAC: 00000015
>
> Backtrace:
> [<c0500e5c>] (leaf_walk_rcu+0x10/0xa0) from [<c050108c>]
> (fib_route_seq_next+0x58/0x74)
> [<c050108c>] (fib_route_seq_next+0x58/0x74) from [<c011c06c>]
> (seq_read+0x2cc/0x438)
> [<c011c06c>] (seq_read+0x2cc/0x438) from [<c0145734>]
> (proc_reg_read+0xb0/0xcc)
> [<c0145734>] (proc_reg_read+0xb0/0xcc) from [<c0100798>]
> (vfs_read+0xac/0x124)
> [<c0100798>] (vfs_read+0xac/0x124) from [<c0100848>] (sys_read+0x38/0x64)
> [<c0100848>] (sys_read+0x38/0x64) from [<c000e100>]
> (ret_fast_syscall+0x0/0x48)
>
> Thanks,
> Vinayak
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