Hi Paul,
On Mon, 8 July 2024, Paul E. McKenney wrote:
>On Fri, Jun 28, 2024 at 01:18:26PM +0900, takakura@xxxxxxxxxxxxx wrote:
>> From: Ryo Takakura <takakura@xxxxxxxxxxxxx>
>>
>> The commit 2d7f00b2f0130 ("rcu: Suppress smp_processor_id() complaint
>> in synchronize_rcu_expedited_wait()") disabled preemption around
>> dump_cpu_task() to suppress warning on its usage within preemtible context.
>>
>> Calling dump_cpu_task() doesn't required to be in non-preemptible context
>> except for suppressing the smp_processor_id() warning.
>> As the smp_processor_id() is evaluated along with in_hardirq()
>> to check if it's in interrupt context, this patch removes the need
>> for its preemtion disablement by reordering the condition so that
>> smp_processor_id() only gets evaluated when it's in interrupt context.
>>
>> Signed-off-by: Ryo Takakura <takakura@xxxxxxxxxxxxx>
>
>Hearing no objections, I pulled this in for further review and testing.
>
>I had to hand-apply this due to a recent conflicting change in the
>-rcu tree, so could you please check the version below in case I messed
>something up?
>
> Thanx, Paul
Thanks for preparing the patch!
I checked it on the rcu tree and looks good to me.
If possible, could you replace the title with s/rcu_dump_task()/dump_cpu_task()/
when applying?
I made a mistake with the title where dump_cpu_task() is the one being modified,
not rcu_dump_task(). I'm sorry for the confusion.
Sincerely,
Ryo Takakura
>
>------------------------------------------------------------------------
>
>commit ad6647a70f239aa9f2741b2f5a828a4483122a26
>Author: Ryo Takakura <takakura@xxxxxxxxxxxxx>
>Date: Fri Jun 28 13:18:26 2024 +0900
>
> rcu: Let rcu_dump_task() be used without preemption disabled
>
> The commit 2d7f00b2f0130 ("rcu: Suppress smp_processor_id() complaint
> in synchronize_rcu_expedited_wait()") disabled preemption around
> dump_cpu_task() to suppress warning on its usage within preemtible context.
>
> Calling dump_cpu_task() doesn't required to be in non-preemptible context
> except for suppressing the smp_processor_id() warning.
> As the smp_processor_id() is evaluated along with in_hardirq()
> to check if it's in interrupt context, this patch removes the need
> for its preemtion disablement by reordering the condition so that
> smp_processor_id() only gets evaluated when it's in interrupt context.
>
> Signed-off-by: Ryo Takakura <takakura@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
>
>diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
>index d4be644afb50..c5d9a7eb0803 100644
>--- a/kernel/rcu/tree_exp.h
>+++ b/kernel/rcu/tree_exp.h
>@@ -597,9 +597,7 @@ static void synchronize_rcu_expedited_stall(unsigned long jiffies_start, unsigne
> mask = leaf_node_cpu_bit(rnp, cpu);
> if (!(READ_ONCE(rnp->expmask) & mask))
> continue;
>- preempt_disable(); // For smp_processor_id() in dump_cpu_task().
> dump_cpu_task(cpu);
>- preempt_enable();
> }
> rcu_exp_print_detail_task_stall_rnp(rnp);
> }
>diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>index 05afa2932b5e..bdb0e0328f6a 100644
>--- a/kernel/sched/core.c
>+++ b/kernel/sched/core.c
>@@ -11485,7 +11485,7 @@ struct cgroup_subsys cpu_cgrp_subsys = {
>
> void dump_cpu_task(int cpu)
> {
>- if (cpu == smp_processor_id() && in_hardirq()) {
>+ if (in_hardirq() && cpu == smp_processor_id()) {
> struct pt_regs *regs;
>
> regs = get_irq_regs();
