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Message-ID: <20110121172420.7ac74133@chocolatine.cbg.collabora.co.uk>
Date: Fri, 21 Jan 2011 17:24:20 +0000
From: Alban Crequy <alban.crequy@...labora.co.uk>
To: Alban Crequy <alban.crequy@...labora.co.uk>
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <eric.dumazet@...il.com>,
Lennart Poettering <lennart@...ttering.net>,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Ian Molton <ian.molton@...labora.co.uk>
Subject: Re: [PATCH 5/8] af_unix: find the recipients of a multicast group
[drop Cc on linux-doc]
I've got a this message with my multicast patches:
[ 109.314741] =================================
[ 109.316007] [ INFO: inconsistent lock state ]
[ 109.316007] 2.6.38-rc1+ #14
[ 109.316007] ---------------------------------
[ 109.316007] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[ 109.316007] ksoftirqd/1/9 [HC0[0]:SC1[1]:HE0:SE0] takes:
[ 109.316007] (&af_unix_sk_receive_queue_lock_key){+.?...}, at: [<c1256028>] skb_dequeue+0x12/0x4a
[ 109.316007] {SOFTIRQ-ON-W} state was registered at:
[ 109.316007] [<c105b9b9>] __lock_acquire+0x2df/0xb95
[ 109.316007] [<c105c334>] lock_acquire+0xc5/0xe6
[ 109.316007] [<c12fd21d>] _raw_spin_lock+0x33/0x40
[ 109.316007] [<e080cbc8>] unix_stream_connect+0x34f/0x3d5 [unix]
[ 109.316007] [<c1250918>] sys_connect+0x7c/0xb2
[ 109.316007] [<c125169e>] sys_socketcall+0xb0/0x289
[ 109.316007] [<c12fdb4c>] syscall_call+0x7/0xb
[ 109.316007] irq event stamp: 463879
[ 109.316007] hardirqs last enabled at (463878): [<c10c8d3c>] kmem_cache_free+0xa4/0xe2
[ 109.316007] hardirqs last disabled at (463879): [<c12fd2ed>] _raw_spin_lock_irqsave+0x1d/0x57
[ 109.316007] softirqs last enabled at (463638): [<c10385d9>] __do_softirq+0x17c/0x190
[ 109.316007] softirqs last disabled at (463641): [<c1004bd3>] do_softirq+0x60/0xb9
[ 109.316007]
[ 109.316007] other info that might help us debug this:
[ 109.316007] no locks held by ksoftirqd/1/9.
[ 109.316007]
[ 109.316007] stack backtrace:
[ 109.316007] Pid: 9, comm: ksoftirqd/1 Not tainted 2.6.38-rc1+ #14
[ 109.316007] Call Trace:
[ 109.316007] [<c105a70f>] ? valid_state+0x168/0x174
[ 109.316007] [<c105a803>] ? mark_lock+0xe8/0x1e8
[ 109.316007] [<c105aefb>] ? check_usage_forwards+0x0/0x77
[ 109.316007] [<c105b94b>] ? __lock_acquire+0x271/0xb95
[ 109.316007] [<c1059af3>] ? register_lock_class+0x17/0x2a4
[ 109.316007] [<c105a739>] ? mark_lock+0x1e/0x1e8
[ 109.316007] [<c1059787>] ? trace_hardirqs_off+0xb/0xd
[ 109.316007] [<c105ace5>] ? debug_check_no_locks_freed+0x115/0x12d
[ 109.316007] [<c1256028>] ? skb_dequeue+0x12/0x4a
[ 109.316007] [<c105c334>] ? lock_acquire+0xc5/0xe6
[ 109.316007] [<c1256028>] ? skb_dequeue+0x12/0x4a
[ 109.316007] [<c12fd317>] ? _raw_spin_lock_irqsave+0x47/0x57
[ 109.316007] [<c1256028>] ? skb_dequeue+0x12/0x4a
[ 109.316007] [<c1256028>] ? skb_dequeue+0x12/0x4a
[ 109.316007] [<c1256a75>] ? skb_queue_purge+0x14/0x1b
[ 109.316007] [<e080cc62>] ? unix_sock_destructor+0x14/0xb6 [unix]
[ 109.316007] [<c12532fe>] ? __sk_free+0x17/0x13f
[ 109.316007] [<c105ab89>] ? trace_hardirqs_on_caller+0xeb/0x125
[ 109.316007] [<c1253488>] ? sk_free+0x16/0x18
[ 109.316007] [<e0809f74>] ? sock_put+0x13/0x15 [unix]
[ 109.316007] [<e080a107>] ? kfree_sock_set+0x21/0x36 [unix]
[ 109.316007] [<e080a127>] ? sock_set_reclaim+0xb/0xd [unix]
[ 109.316007] [<c1080068>] ? __rcu_process_callbacks+0x176/0x26b
[ 109.316007] [<c108017b>] ? rcu_process_callbacks+0x1e/0x3b
[ 109.316007] [<c103850e>] ? __do_softirq+0xb1/0x190
[ 109.316007] [<c103845d>] ? __do_softirq+0x0/0x190
[ 109.316007] <IRQ> [<c1037d27>] ? run_ksoftirqd+0x57/0xd3
[ 109.316007] [<c1037cd0>] ? run_ksoftirqd+0x0/0xd3
[ 109.316007] [<c104a930>] ? kthread+0x6d/0x72
[ 109.316007] [<c104a8c3>] ? kthread+0x0/0x72
[ 109.316007] [<c1003742>] ? kernel_thread_helper+0x6/0x10
The socket is released and skb is dequeued in a call_rcu() callback:
> + /* Take the lock to insert the new list but take the opportunity to do
> + * some garbage collection on outdated lists */
> + spin_lock(&unix_multicast_lock);
> + hlist_for_each_entry_rcu(del_set, pos, &group->mcast_members_lists,
> + list) {
> + if (down_trylock(&del_set->sem)) {
> + /* the list is being used by someone else */
> + continue;
> + }
> + if (del_set->generation < generation) {
> + hlist_del_rcu(&del_set->list);
> + call_rcu(&del_set->rcu, sock_set_reclaim);
The purpose of that chunk is to release outdated struct sock_set soon
enough instead of doing it in destroy_mcast_group(). So senders of
multicast messages don't have to iterate on outdated sock_set when
they are looking for an available set of sockets.
In af_unix.c, lockdep annotations (a09785a2):
/*
* AF_UNIX sockets do not interact with hardware, hence they
* dont trigger interrupts - so it's safe for them to have
* bh-unsafe locking for their sk_receive_queue.lock. Split off
* this special lock-class by reinitializing the spinlock key:
*/
static struct lock_class_key af_unix_sk_receive_queue_lock_key;
lockdep_set_class(&sk->sk_receive_queue.lock,
&af_unix_sk_receive_queue_lock_key);
I don't know if I should avoid releasing sockets in RCU callbacks or
update the lockdep annotations.
--
Alban
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