Re: 2.6.36-rc5-git1 -- include/linux/netpoll.h:67 invoked rcu_dereference_check() without protection!

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Wed, Sep 22, 2010 at 01:43:26PM -0400, Miles Lane wrote:
> That worked for me.
> Thanks!

Thank you, Eric and Miles!!!

Miles, you tested the version with irqs_disabled(), correct?

I have queued that version, hopefully Ingo will like it better than
he liked my earlier attempts...  ;-)

							Thanx, Paul

>        Miles
> 
> This message sent using my interplanetary mobile messaging device.
> 
> On Sep 22, 2010, at 10:27 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> 
> > Le mercredi 22 septembre 2010 à 08:38 +0200, Eric Dumazet a écrit :
> >> Le mercredi 22 septembre 2010 à 00:22 -0400, Miles Lane a écrit :
> >>> [ INFO: suspicious rcu_dereference_check() usage. ]
> >>> ---------------------------------------------------
> >>> include/linux/netpoll.h:67 invoked rcu_dereference_check() without protection!
> >>> 
> >>> other info that might help us debug this:
> >>> 
> >>> 
> >>> rcu_scheduler_active = 1, debug_locks = 1
> >>> 1 lock held by avahi-daemon/1597:
> >>> #0:  (sk_lock-AF_INET6){+.+.+.}, at: [<ffffffffa03673b7>]
> >>> udpv6_sendmsg+0x6c2/0x9e6 [ipv6]
> >>> 
> >>> stack backtrace:
> >>> Pid: 1597, comm: avahi-daemon Not tainted 2.6.36-rc5 #13
> >>> Call Trace:
> >>> [<ffffffff810618d7>] lockdep_rcu_dereference+0x9d/0xa6
> >>> [<ffffffff8129d543>] netif_rx+0x4e/0x1a7
> >>> [<ffffffff8102fe4e>] ? get_parent_ip+0x11/0x41
> >>> [<ffffffff8129d7e3>] netif_rx_ni+0x1e/0x58
> >>> [<ffffffffa0352d50>] ip6_dev_loopback_xmit+0xc0/0xc7 [ipv6]
> >>> [<ffffffffa0352ef0>] ip6_finish_output2+0x199/0x3b6 [ipv6]
> >>> [<ffffffffa035401c>] ip6_finish_output+0xf0f/0xf27 [ipv6]
> >>> [<ffffffff8131e08a>] ? csum_partial_copy_from_user+0xb4/0xea
> >>> [<ffffffff812968a8>] ? csum_partial_copy_fromiovecend+0x178/0x1bd
> >>> [<ffffffffa035418c>] ip6_output+0x158/0x161 [ipv6]
> >>> [<ffffffff8102fe4e>] ? get_parent_ip+0x11/0x41
> >>> [<ffffffffa035262d>] ip6_local_out+0x5d/0x62 [ipv6]
> >>> [<ffffffffa0352a98>] ip6_push_pending_frames+0x466/0x524 [ipv6]
> >>> [<ffffffffa0366a93>] udp_v6_push_pending_frames+0x27f/0x2fb [ipv6]
> >>> [<ffffffffa03673b7>] ? udpv6_sendmsg+0x6c2/0x9e6 [ipv6]
> >>> [<ffffffffa03674ba>] udpv6_sendmsg+0x7c5/0x9e6 [ipv6]
> >>> [<ffffffff812fb634>] ? inet_sendmsg+0x0/0x11f
> >>> [<ffffffff812fb746>] inet_sendmsg+0x112/0x11f
> >>> [<ffffffff812fb634>] ? inet_sendmsg+0x0/0x11f
> >>> [<ffffffff8128ca91>] sock_sendmsg+0xe7/0x108
> >>> [<ffffffff810a4c3b>] ? might_fault+0x63/0xb3
> >>> [<ffffffff810a4c84>] ? might_fault+0xac/0xb3
> >>> [<ffffffff810a4c3b>] ? might_fault+0x63/0xb3
> >>> [<ffffffff8128d346>] sys_sendmsg+0x24f/0x2d6
> >>> [<ffffffff8102fe4e>] ? get_parent_ip+0x11/0x41
> >>> [<ffffffff81031ef7>] ? sub_preempt_count+0x92/0xa6
> >>> [<ffffffff810570ce>] ? __srcu_read_unlock+0x3b/0x57
> >>> [<ffffffff81001f9c>] ? sysret_check+0x27/0x62
> >>> [<ffffffff81001f6b>] system_call_fastpath+0x16/0x1b#
> >> 
> >> Oh well.
> >> 
> >> Thanks for the report. Could you please test following patch ?
> >> 
> >> 
> >> [PATCH] rcu: rcu_dereference_bh() is hard irq safe
> >> 
> >> rcu_dereference_bh() doesnt know yet about hard irq being disabled, so
> >> lockdep can trigger in netpoll_rx() after commit f0f9deae9e7c4 (netpoll:
> >> Disable IRQ around RCU dereference in netpoll_rx)
> >> 
> >> Reported-by: Miles Lane <miles.lane@gmail.com>
> >> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> >> ---
> >> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> >> index 9fbc54a..435c502 100644
> >> --- a/include/linux/rcupdate.h
> >> +++ b/include/linux/rcupdate.h
> >> @@ -454,7 +454,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
> >>  * Makes rcu_dereference_check() do the dirty work.
> >>  */
> >> #define rcu_dereference_bh(p) \
> >> -        rcu_dereference_check(p, rcu_read_lock_bh_held())
> >> +        rcu_dereference_check(p, rcu_read_lock_bh_held() || in_irq())
> > 
> > oops, I meant irqs_disabled() here, not in_irq()
> > 
> >> 
> >> /**
> >>  * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
> >> 
> > 
> >