On Tue, Nov 27, 2012 at 04:39:59PM +0100, Frederic Weisbecker wrote: > 2012/11/27 Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>: > > I noticed some warnings complaining about dynticks_nesting value, like > > > > [ 267.545032] ------------[ cut here ]------------ > > [ 267.545032] WARNING: at kernel/rcutree.c:382 rcu_eqs_enter+0xab/0xc0() > > [ 267.545032] Hardware name: Bochs > > [ 267.545032] Modules linked in: > > [ 267.545032] Pid: 0, comm: swapper/2 Not tainted 3.7.0-rc5-next-20121115 #8 > > [ 267.545032] Call Trace: > > [ 267.545032] [<ffffffff8104714f>] warn_slowpath_common+0x7f/0xc0 > > [ 267.545032] [<ffffffff810471aa>] warn_slowpath_null+0x1a/0x20 > > [ 267.545032] [<ffffffff810e607b>] rcu_eqs_enter+0xab/0xc0 > > [ 267.545032] [<ffffffff810e60bb>] rcu_idle_enter+0x2b/0x70 > > [ 267.545032] [<ffffffff8100d44f>] cpu_idle+0x6f/0x100 > > [ 267.545032] [<ffffffff814bf055>] start_secondary+0x205/0x20c > > [ 267.545032] ---[ end trace 924ae80da035028d ]--- > > > > After enabling rcu-dyntick tracing, I got following abnormal > > dynticks_nesting values (13fffffffffffff, ff00000000000001,etc): > > ... > > 1 <idle>-0 [002] dN.2 18739.518567: rcu_dyntick: End 0 140000000000000 rcu_idle_exit > > 2 sshd-696 [002] d..1 18739.518675: rcu_dyntick: ++= 140000000000000 140000000000001 rcu_irq_enter - apf (not present) > > > > 3 <idle>-0 [002] d..2 18739.518705: rcu_dyntick: Start 140000000000001 0 rcu_idle_enter > > 4 <idle>-0 [002] d..2 18739.521252: rcu_dyntick: End 0 1 rcu_irq_enter - apf (page ready) > > 5 <idle>-0 [002] dN.2 18739.521261: rcu_dyntick: Start 1 0 rcu_irq_exit - apf (page ready) > > 6 <idle>-0 [002] dN.2 18739.521263: rcu_dyntick: End 0 140000000000000 rcu_idle_exit > > > > 7 sshd-696 [002] d..1 18739.521299: rcu_dyntick: --= 140000000000000 13fffffffffffff rcu_irq_exit - apf (not present) > > Calling rcu_irq_exit() without a matching rcu_irq_enter() after the > last rcu_idle_exit() is illegal, isn't it? It is OK to call rcu_irq_exit() without a matching rcu_irq_enter() -only- if you have also called rcu_idle_exit() since the last rcu_idle_enter(). There will be a similar rule for rcu_user_exit(). More generally, it is OK to call rcu_irq_exit() without a matching rcu_irq_enter() only if RCU believes that the CPU you are running on is non-idle. On 32-bit systems, you are only allowed a few tens of million such unmatched rcu_irq_enter() calls in a given RCU-non-idle region. All courtesy of RCU's need to tolerate architectures that enter interrupt handlers without ever leaving them and vice versa. ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
