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" <paul...@linux.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 <paul...@linux.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.
Thanx, Paul
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