linux-kernel - Re: [PATCH 10/11] sched: Debug nested sleeps

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Message-ID: <20140929221344.GB12112@redhat.com>
Date:	Tue, 30 Sep 2014 00:13:44 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, torvalds@...ux-foundation.org,
	tglx@...utronix.de, ilya.dryomov@...tank.com,
	umgwanakikbuti@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/11] sched: Debug nested sleeps

On 09/24, Peter Zijlstra wrote:
>
> +#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
> +
> +#define __set_task_state(tsk, state_value)			\
> +	do {							\
> +		(tsk)->task_state_change = _THIS_IP_;		\
> +		(tsk)->state = (state_value);			\
> +	} while (0)

...

> @@ -7143,6 +7143,19 @@ void __might_sleep(const char *file, int
>  {
>  	static unsigned long prev_jiffy;	/* ratelimiting */
>
> +	/*
> +	 * Blocking primitives will set (and therefore destroy) current->state,
> +	 * since we will exit with TASK_RUNNING make sure we enter with it,
> +	 * otherwise we will destroy state.
> +	 */
> +	if (WARN(current->state != TASK_RUNNING,
> +			"do not call blocking ops when !TASK_RUNNING; "
> +			"state=%lx set at [<%p>] %pS\n",
> +			current->state,
> +			(void *)current->task_state_change,
> +			(void *)current->task_state_change))
> +		__set_current_state(TASK_RUNNING);

Question: now that we have ->task_state_change, perhaps it makes sense
to redefine fixup_sleep()

	#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
	#define fixup_sleep()	(current->task_state_change = 0)
	#else
	#define fixup_sleep()	do { } while (0)
	#endif

and make the WARN() above depend on task_state_change != 0 ?

This is minor, but this way CONFIG_DEBUG_ATOMIC_SLEEP will not imply
a subtle behavioural change.

Oleg.

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