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SubjectRe: [PATCH tip/core/urgent 1/2] rcu: Prevent soft-lockup complaints about no-CBs CPUs
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Hi Paul,

2013/1/5 Paul E. McKenney <paulmck@linux.vnet.ibm.com>:
> From: Paul Gortmaker <paul.gortmaker@windriver.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@gmail.com>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
> Signed-off-by: Paul E. McKenney <paulmck@linux.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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