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[PATCH] rcu: Let rcu_dump_task() be used without preemption disabled

takakura@valinux.co.jp posted 1 patch 1 year, 5 months ago 
kernel/rcu/tree_exp.h | 2 --
kernel/sched/core.c   | 2 +-
2 files changed, 1 insertion(+), 3 deletions(-)
[PATCH] rcu: Let rcu_dump_task() be used without preemption disabled
Posted by takakura@valinux.co.jp 1 year, 5 months ago 
From: Ryo Takakura <takakura@valinux.co.jp>

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@valinux.co.jp>
---
 kernel/rcu/tree_exp.h | 2 --
 kernel/sched/core.c   | 2 +-
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 8a1d9c8bd9f7..80c461b26144 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -617,9 +617,7 @@ static void synchronize_rcu_expedited_wait(void)
 				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 bcf2c4cc0522..38efbdafe3d4 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();
-- 
2.34.1
Re: [PATCH] rcu: Let rcu_dump_task() be used without preemption disabled
Posted by Paul E. McKenney 1 year, 5 months ago 
On Fri, Jun 28, 2024 at 01:18:26PM +0900, takakura@valinux.co.jp wrote:
> From: Ryo Takakura <takakura@valinux.co.jp>
> 
> 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@valinux.co.jp>

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

------------------------------------------------------------------------

commit ad6647a70f239aa9f2741b2f5a828a4483122a26
Author: Ryo Takakura <takakura@valinux.co.jp>
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@valinux.co.jp>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

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();
Re: [PATCH] rcu: Let rcu_dump_task() be used without preemption disabled
Posted by takakura@valinux.co.jp 1 year, 5 months ago 
Hi Paul,

On Mon, 8 July 2024, Paul E. McKenney wrote:
>On Fri, Jun 28, 2024 at 01:18:26PM +0900, takakura@valinux.co.jp wrote:
>> From: Ryo Takakura <takakura@valinux.co.jp>
>> 
>> 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@valinux.co.jp>
>
>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@valinux.co.jp>
>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@valinux.co.jp>
>    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>
>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();
Re: [PATCH] rcu: Let rcu_dump_task() be used without preemption disabled
Posted by Paul E. McKenney 1 year, 5 months ago 
On Tue, Jul 09, 2024 at 02:34:26PM +0900, takakura@valinux.co.jp wrote:
> Hi Paul,
> 
> On Mon, 8 July 2024, Paul E. McKenney wrote:
> >On Fri, Jun 28, 2024 at 01:18:26PM +0900, takakura@valinux.co.jp wrote:
> >> From: Ryo Takakura <takakura@valinux.co.jp>
> >> 
> >> 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@valinux.co.jp>
> >
> >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.

Thank you for calling my attention to this.

Done locally, and it will show up on my next rebase.

								Thanx, Paul

> Sincerely,
> Ryo Takakura
> 
> >
> >------------------------------------------------------------------------
> >
> >commit ad6647a70f239aa9f2741b2f5a828a4483122a26
> >Author: Ryo Takakura <takakura@valinux.co.jp>
> >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@valinux.co.jp>
> >    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> >
> >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();

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