linux-kernel - Re: [RFC][PATCH 03/11] sched: Robustify preemption leak checks

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Message-ID: <20150929110734.2f06e07a@gandalf.local.home>
Date:	Tue, 29 Sep 2015 11:07:34 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, fweisbec@...il.com, oleg@...hat.com,
	umgwanakikbuti@...il.com, tglx@...utronix.de
Subject: Re: [RFC][PATCH 03/11] sched: Robustify preemption leak checks

On Tue, 29 Sep 2015 11:28:28 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> When we warn about a preempt_count leak; reset the preempt_count to
> the known good value such that the problem does not ripple forward.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/exit.c       |    4 +++-
>  kernel/sched/core.c |    4 +++-
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -706,10 +706,12 @@ void do_exit(long code)
>  	smp_mb();
>  	raw_spin_unlock_wait(&tsk->pi_lock);
>  
> -	if (unlikely(in_atomic()))
> +	if (unlikely(in_atomic())) {
>  		pr_info("note: %s[%d] exited with preempt_count %d\n",
>  			current->comm, task_pid_nr(current),
>  			preempt_count());
> +		preempt_count_set(PREEMPT_ENABLED);
> +	}

Looks good.

>  
>  	/* sync mm's RSS info before statistics gathering */
>  	if (tsk->mm)
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2960,8 +2960,10 @@ static inline void schedule_debug(struct
>  	 * schedule() atomically, we ignore that path. Otherwise whine
>  	 * if we are scheduling when we should not.
>  	 */
> -	if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD))
> +	if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD)) {
>  		__schedule_bug(prev);
> +		preempt_count_set(PREEMPT_DISABLED);
> +	}

Of course, if this was not a preemption leak, but something that called
schedule within a preempt_disable()/preempt_enable() section, when it
returns, preemption will be enabled, right?

-- Steve


>  	rcu_sleep_check();
>  
>  	profile_hit(SCHED_PROFILING, __builtin_return_address(0));
> 

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