linux-kernel - Re: INFO: possible circular locking dependency detected

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <201107150735.50478.edt@aei.ca>
Date:	Fri, 15 Jul 2011 07:35:49 -0400
From:	Ed Tomlinson <edt@....ca>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	paulmck@...ux.vnet.ibm.com, Steven Rostedt <rostedt@...dmis.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: INFO: possible circular locking dependency detected

On Friday 15 July 2011 07:29:22 Peter Zijlstra wrote:
> On Fri, 2011-07-15 at 07:05 -0400, Ed Tomlinson wrote:
> > Jul 14 23:21:18 grover kernel: [  920.659426] -> #1 (rcu_node_level_0){..-...}:
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8108b7e5>] lock_acquire+0x95/0x140
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8157808b>] _raw_spin_lock+0x3b/0x50
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff810ba797>] __rcu_read_unlock+0x197/0x2d0
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8103f2f5>] select_task_rq_fair+0x585/0xa80
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8104633b>] try_to_wake_up+0x17b/0x360
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff81046575>] wake_up_process+0x15/0x20
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff810528f4>] irq_exit+0xb4/0x100
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff8158197e>] smp_apic_timer_interrupt+0x6e/0x99
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff81580c53>] apic_timer_interrupt+0x13/0x20
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff810ba6e9>] __rcu_read_unlock+0xe9/0x2d0 
> > Jul 14 23:21:18 grover kernel: [  920.659426]        [<ffffffff814c20d4>] sock_def_readable+0x94/0xc0
> 
> Ed, are you perchance running with force_irqthreads?

Yes.  

I'm off to work - will test any patches when I get back in 8-10 hours.

Thanks
Ed

> Paul, what appears to be happening here is that some rcu_read_unlock()
> gets interrupted, possibly before calling rcu_read_unlock_special(),
> possibly not if the interrupt is itself the timer interrupt.
> 
> Supposing ->rcu_read_unlock_special is set before, any wakeup happening
> from an interrupt hitting __rcu_read_unlock():
> 
> void __rcu_read_unlock(void)
> {
>         struct task_struct *t = current;
>                 
>         barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
>         --t->rcu_read_lock_nesting;
>         barrier();  /* decrement before load of ->rcu_read_unlock_special */
>         if (t->rcu_read_lock_nesting == 0 &&
>             unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
>                 rcu_read_unlock_special(t);
> #ifdef CONFIG_PROVE_LOCKING
>         WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
> #endif /* #ifdef CONFIG_PROVE_LOCKING */
> }
> 
> After --t->rcu_read_lock_nesting, but before calling
> rcu_read_unlock_special(), will trigger this lock inversion.
> 
> The alternative case, ->rcu_read_unlock_special is not set yet, it can
> be set if the interrupt hitting in that same spot above, is the timer
> interrupt, and the wakeup happens either from the softirq ran from the
> hard IRQ tail, or as I suspect here happens, the wakeup of ksoftirqd/#.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/