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
| ||
|
Date: Fri, 15 Jul 2011 15:07:39 +0200 From: Peter Zijlstra <a.p.zijlstra@...llo.nl> To: paulmck@...ux.vnet.ibm.com Cc: Ed Tomlinson <edt@....ca>, 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 Fri, 2011-07-15 at 05:42 -0700, Paul E. McKenney wrote: > On Fri, Jul 15, 2011 at 01:29:22PM +0200, 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? > > > > 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/#. OK, so the latter case cannot happen (rcu_preempt_check_callbacks only sets NEED_QS when rcu_read_lock_nesting), we need two interrupts for this to happen. rcu_read_lock() <IRQ> |= RCU_READ_UNLOCK_NEED_QS rcu_read_unlock() __rcu_read_unlock() --rcu_read_lock_nesting; <IRQ> ttwu() rcu_read_lock() rcu_read_unlock() rcu_read_unlock_special() *BANG* rcu_read_unlock_special() -- 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/
Powered by blists - more mailing lists