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Date: Tue, 5 May 2015 11:45:04 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Sasha Levin <sasha.levin@...cle.com> Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com Subject: Re: [PATCH tip/core/rcu 2/2] rcu: Tighten up affinity and check for sysidle On Tue, May 05, 2015 at 12:27:21AM -0700, Paul E. McKenney wrote: > On Mon, May 04, 2015 at 06:10:31PM -0400, Sasha Levin wrote: > > On 03/03/2015 12:50 PM, Paul E. McKenney wrote: > > > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> > > > > > > If the RCU grace-period kthread invoking rcu_sysidle_check_cpu() > > > happens to be running on the tick_do_timer_cpu initially, > > > then rcu_bind_gp_kthread() won't bind it. This kthread might > > > then migrate before invoking rcu_gp_fqs(), which will trigger the > > > WARN_ON_ONCE() in rcu_sysidle_check_cpu(). This commit therefore makes > > > rcu_bind_gp_kthread() do the binding even if the kthread is currently > > > on the same CPU. Because this incurs added overhead, this commit also > > > causes each RCU grace-period kthread to invoke rcu_bind_gp_kthread() > > > once at boot rather than at the beginning of each grace period. > > > And as long as rcu_bind_gp_kthread() is being modified, this commit > > > eliminates its #ifdef. > > > > > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > > > --- > > > kernel/rcu/tree.c | 2 +- > > > kernel/rcu/tree_plugin.h | 12 ++++++------ > > > 2 files changed, 7 insertions(+), 7 deletions(-) > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > index 735bd7ee749a..a6972c20eaa5 100644 > > > --- a/kernel/rcu/tree.c > > > +++ b/kernel/rcu/tree.c > > > @@ -1707,7 +1707,6 @@ static int rcu_gp_init(struct rcu_state *rsp) > > > struct rcu_node *rnp = rcu_get_root(rsp); > > > > > > ACCESS_ONCE(rsp->gp_activity) = jiffies; > > > - rcu_bind_gp_kthread(); > > > raw_spin_lock_irq(&rnp->lock); > > > smp_mb__after_unlock_lock(); > > > if (!ACCESS_ONCE(rsp->gp_flags)) { > > > @@ -1895,6 +1894,7 @@ static int __noreturn rcu_gp_kthread(void *arg) > > > struct rcu_state *rsp = arg; > > > struct rcu_node *rnp = rcu_get_root(rsp); > > > > > > + rcu_bind_gp_kthread(); > > > for (;;) { > > > > > > /* Handle grace-period start. */ > > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > > > index 0a571e9a0f1d..b46c92824db1 100644 > > > --- a/kernel/rcu/tree_plugin.h > > > +++ b/kernel/rcu/tree_plugin.h > > > @@ -2763,7 +2763,8 @@ static void rcu_sysidle_exit(int irq) > > > > > > /* > > > * Check to see if the current CPU is idle. Note that usermode execution > > > - * does not count as idle. The caller must have disabled interrupts. > > > + * does not count as idle. The caller must have disabled interrupts, > > > + * and must be running on tick_do_timer_cpu. > > > */ > > > static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, > > > unsigned long *maxj) > > > @@ -2784,8 +2785,8 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, > > > if (!*isidle || rdp->rsp != rcu_state_p || > > > cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) > > > return; > > > - if (rcu_gp_in_progress(rdp->rsp)) > > > - WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); > > > + /* Verify affinity of current kthread. */ > > > + WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); > > > > Hey Paul, > > > > I seem to be hitting this warning: > > > > [22408.472078] ------------[ cut here ]------------ > > [22408.476972] WARNING: CPU: 1 PID: 8 at kernel/rcu/tree_plugin.h:2796 rcu_sysidle_check_cpu+0x374/0x3f0() > > [22408.481567] Modules linked in: > > [22408.486054] CPU: 1 PID: 8 Comm: rcu_sched Tainted: G W 4.1.0-rc1-next-20150504+ #3 > > [22408.490576] Hardware name: Oracle Corporation OVCA X3-2 /ASSY,MOTHERBOARD,1U , BIOS 17021300 06/19/2012 > > [22408.495117] ffff881ff2db4600 0000000044d8814b ffff881ff2f1fab8 ffffffff830f9926 > > [22408.499647] 0000000000000000 0000000000000000 ffff881ff2f1fb08 ffffffff8120bed0 > > [22408.504120] ffff881ff2f1fb88 ffffffff81324ec4 1ffff103fe5e3f65 ffff881ff2f1fd48 > > [22408.508568] Call Trace: > > [22408.512953] dump_stack (lib/dump_stack.c:52) > > [22408.517331] warn_slowpath_common (kernel/panic.c:447) > > [22408.521637] ? rcu_sysidle_check_cpu (kernel/rcu/tree_plugin.h:2796 (discriminator 53)) > > [22408.525899] warn_slowpath_null (kernel/panic.c:481) > > [22408.530105] rcu_sysidle_check_cpu (kernel/rcu/tree_plugin.h:2796 (discriminator 53)) > > [22408.534287] ? console_conditional_schedule (kernel/time/timer.c:1472) > > [22408.538413] dyntick_save_progress_counter (kernel/rcu/tree.c:1041) > > [22408.542486] force_qs_rnp (kernel/rcu/tree.c:2793) > > [22408.546504] ? wake_up_atomic_t (kernel/sched/wait.c:200) > > [22408.550461] ? rcu_sysidle_check_cpu (kernel/rcu/tree.c:1039) > > [22408.554374] rcu_gp_kthread (kernel/rcu/tree.c:1914 include/linux/jump_label.h:125 include/linux/context_tracking_state.h:28 include/linux/tick.h:123 kernel/rcu/tree_plugin.h:2914 kernel/rcu/tree.c:1916 kernel/rcu/tree.c:2075) > > [22408.558240] ? rcu_oom_notify (kernel/rcu/tree.c:2012) > > [22408.562044] ? finish_task_switch (include/linux/tick.h:179 kernel/sched/core.c:2248) > > [22408.565789] ? __schedule (kernel/sched/core.c:2340 kernel/sched/core.c:2798) > > [22408.569473] ? __wake_up_common (kernel/sched/wait.c:73) > > [22408.573088] ? prepare_to_wait_event (kernel/sched/wait.c:292) > > [22408.576665] ? rcu_oom_notify (kernel/rcu/tree.c:2012) > > [22408.580197] kthread (kernel/kthread.c:207) > > [22408.583652] ? arch_vtime_task_switch (kernel/sched/cputime.c:753) > > [22408.587065] ? kthread_create_on_node (kernel/kthread.c:176) > > [22408.590427] ? kthread_create_on_node (kernel/kthread.c:176) > > [22408.593713] ret_from_fork (arch/x86/kernel/entry_64.S:640) > > [22408.596972] ? kthread_create_on_node (kernel/kthread.c:176) > > That is certainly not what I wanted to happen! ;-) > > Looking into it. Could you please send along your .CONFIG? Thanx, Paul -- 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/
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