linux-kernel - Re: [Patch 4/7] softirq: Use hotplug thread infrastructure

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Date:	Sat, 21 Jul 2012 10:21:51 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [Patch 4/7] softirq: Use hotplug thread infrastructure

On Mon, Jul 16, 2012 at 10:42:37AM -0000, Thomas Gleixner wrote:
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  kernel/softirq.c |  107 +++++++++++++------------------------------------------
>  1 file changed, 26 insertions(+), 81 deletions(-)

This is also much more compact!  One issue with fix below.

							Thanx, Paul

[ . . . ]

> +static void run_ksoftirqd(unsigned int cpu)
> +{
> +	local_irq_disable();
> +	if (local_softirq_pending()) {
> +		__do_softirq();
> +		local_irq_enable();
> +		cond_resched();
> +		rcu_note_context_switch(cpu);

The rcu_note_context_switch() function must run with preemption disabled.
I fixed this as follows:

+static void run_ksoftirqd(unsigned int cpu)
+{
+	local_irq_disable();
+	if (local_softirq_pending()) {
+		__do_softirq();
+		rcu_note_context_switch(cpu);
+		local_irq_enable();
+		cond_resched();
+		return;
 	}

Again, I also placed the updated series on -rcu at branch rcu/smp/hotplug
(git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git),
based on tip/smp/hotplug, for Linaro testing purposes.

With these two changes, this series merged with Tejun's workqueue
hotplug changes merged with my -rcu tree passed moderate rcutorture
and hotplug testing, with the exception of some apparently unrelated
build problems in UP configuration:

warning: call to ‘copy_from_user_overflow’ declared with attribute warning: copy_from_user() buffer size is not provably correct [enabled by default

I have a fix for an earlier occurrence of this problem that I will try next.

							Thanx, Paul

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