linux-kernel - Re: [PATCH] scheduler: convert BUG_ON()s in try_to_wake_up_local() to WARN_ON

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Date:	Mon, 18 Mar 2013 15:32:20 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <clark@...hat.com>
Subject: Re: [PATCH] scheduler: convert BUG_ON()s in try_to_wake_up_local()
 to WARN_ON_ONCE()s

On Mon, 2013-03-18 at 12:22 -0700, Tejun Heo wrote:
> try_to_wake_up_local() should only be invoked to wake up another task
> in the same runqueue and BUG_ON()s are used to enforce the rule.
> Missing try_to_wake_up_local() can stall workqueue execution but such
> stalls are likely to be finite either by another work item being
> queued or the one blocked getting unblocked.  There's no reason to
> trigger BUG while holding rq lock crashing the whole system.
> 
> Convert BUG_ON()s in try_to_wake_up_local() to WARN_ON_ONCE()s.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> ---
>  kernel/sched/core.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 7f12624..a2eda4d 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1498,8 +1498,10 @@ static void try_to_wake_up_local(struct task_struct *p)
>  {
>  	struct rq *rq = task_rq(p);
>  
> -	BUG_ON(rq != this_rq());
> -	BUG_ON(p == current);
> +	if (WARN_ON_ONCE(rq != this_rq()) ||
> +	    WARN_ON_ONCE(p == current))
> +		return;
> +
>  	lockdep_assert_held(&rq->lock);
>  
>  	if (!raw_spin_trylock(&p->pi_lock)) {


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