linux-kernel - Re: [PATCH tip/core/urgent 1/2] rcu: Prevent soft-lockup complaints about no-CBs CPUs

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Message-ID: <CAFTL4hyYh=C6-jPBm0pWjn2xeDRGtYVGYD46hSr=OfPjNtuDGg@mail.gmail.com>
Date:	Sat, 5 Jan 2013 18:21:01 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, sbw@....edu,
	patches@...aro.org, Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH tip/core/urgent 1/2] rcu: Prevent soft-lockup complaints
 about no-CBs CPUs

Hi Paul,

2013/1/5 Paul E. McKenney <paulmck@...ux.vnet.ibm.com>:
> From: Paul Gortmaker <paul.gortmaker@...driver.com>
>
> The wait_event() at the head of the rcu_nocb_kthread() can result in
> soft-lockup complaints if the CPU in question does not register RCU
> callbacks for an extended period.  This commit therefore changes
> the wait_event() to a wait_event_interruptible().
>
> Reported-by: Frederic Weisbecker <fweisbec@...il.com>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  kernel/rcutree_plugin.h |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> index f6e5ec2..43dba2d 100644
> --- a/kernel/rcutree_plugin.h
> +++ b/kernel/rcutree_plugin.h
> @@ -2366,10 +2366,11 @@ static int rcu_nocb_kthread(void *arg)
>         for (;;) {
>                 /* If not polling, wait for next batch of callbacks. */
>                 if (!rcu_nocb_poll)
> -                       wait_event(rdp->nocb_wq, rdp->nocb_head);
> +                       wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
>                 list = ACCESS_ONCE(rdp->nocb_head);
>                 if (!list) {
>                         schedule_timeout_interruptible(1);
> +                       flush_signals(current);

Why is that needed?
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