Re: [PATCH 1/1] sched: fix the PREEMPT_ACTIVE check in __trace_sched_switch_state()
From: Peter Zijlstra
Date: Fri Oct 10 2014 - 05:55:03 EST
On Tue, Oct 07, 2014 at 09:51:08PM +0200, Oleg Nesterov wrote:
> task_preempt_count() has nothing to do with the actual preempt counter,
> thread_info->saved_preempt_count is only valid right after switch_to().
> __trace_sched_switch_state() can use preempt_count(), prev is still the
> current task when trace_sched_switch() is called.
This is true, but the paranoid in me would like a BUG_ON(p != current)
right along with that to make sure we don't accidentally change this.
But yes, its good to get rid of task_preempt_count(), its horrible.
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> include/trace/events/sched.h | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index 0a68d5a..a7d67bc 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -100,7 +100,7 @@ static inline long __trace_sched_switch_state(struct task_struct *p)
> * For all intents and purposes a preempted task is a running task.
> - if (task_preempt_count(p) & PREEMPT_ACTIVE)
> + if (preempt_count() & PREEMPT_ACTIVE)
> state = TASK_RUNNING | TASK_STATE_MAX;
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