linux-kernel - Re: [PATCH] rcu: Eliminate softirq processing from rcutree

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Date:	Fri, 17 Jan 2014 18:23:19 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Mike Galbraith <bitbucket@...ine.de>
Cc:	paulmck@...ux.vnet.ibm.com, linux-rt-users@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] rcu: Eliminate softirq processing from rcutree

* Mike Galbraith | 2013-12-26 11:03:32 [+0100]:

>On Wed, 2013-12-25 at 04:07 +0100, Mike Galbraith wrote:
>> On Tue, 2013-12-24 at 11:36 -0800, Paul E. McKenney wrote: 
>
>> > So which code do you think deserves the big lump of coal?  ;-)
>> 
>> Sebastian's NO_HZ_FULL locking fixes.
>
>Whack-a-mole hasn't yet dug up any new moles.
>
>---
> kernel/timer.c |    4 ++++
> 1 file changed, 4 insertions(+)
>
>Index: linux-2.6/kernel/timer.c
>===================================================================
>--- linux-2.6.orig/kernel/timer.c
>+++ linux-2.6/kernel/timer.c
>@@ -764,7 +764,9 @@ __mod_timer(struct timer_list *timer, un
> 	timer_stats_timer_set_start_info(timer);
> 	BUG_ON(!timer->function);
> 
>+	local_irq_disable_rt();
> 	base = lock_timer_base(timer, &flags);
>+	local_irq_enable_rt();
> 
> 	ret = detach_if_pending(timer, base, false);
> 	if (!ret && pending_only)
>@@ -1198,7 +1200,9 @@ static inline void __run_timers(struct t
> {
> 	struct timer_list *timer;
> 
>+	local_irq_disable_rt();
> 	spin_lock_irq(&base->lock);
>+	local_irq_enable_rt();
> 	while (time_after_eq(jiffies, base->timer_jiffies)) {
> 		struct list_head work_list;
> 		struct list_head *head = &work_list;
>---
> kernel/time/tick-sched.c |    2 ++
> 1 file changed, 2 insertions(+)

So I had rtmutex-take-the-waiter-lock-with-irqs-off.patch in my queue
which took the waiter lock with irqs off. This should be the same thing
you try do here.

>Index: linux-2.6/kernel/time/tick-sched.c
>===================================================================
>--- linux-2.6.orig/kernel/time/tick-sched.c
>+++ linux-2.6/kernel/time/tick-sched.c
>@@ -216,7 +216,9 @@ void __tick_nohz_full_check(void)
> 
> static void nohz_full_kick_work_func(struct irq_work *work)
> {
>+	local_irq_disable_rt();
> 	__tick_nohz_full_check();
>+	local_irq_enable_rt();
> }

and this should be fixed differently. Since we come from a thread and
check "is current running" but by current we mean a user task and not a
kernel thread.

> 
> static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
>

Sebastian
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