Re: [PATCH tip/core/urgent 1/2] rcu: Prevent soft-lockup complaintsabout no-CBs CPUs

[Frederic Weisbecker]

Hi Paul,

2013/1/5 Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>:
> From: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxx>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> ---
>  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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