linux-kernel - Re: [PATCH RT] sched: drop is_special_task_state() check from __set_current_state_no

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Date:   Wed, 1 Aug 2018 09:19:42 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-rt-users@...r.kernel.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH RT] sched: drop is_special_task_state() check from
 __set_current_state_no_track()

On Wed, 1 Aug 2018 11:05:25 +0200
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> The is_special_task_state() check in __set_current_state_no_track()
> has been wrongly placed. __set_current_state_no_track() is used in RT
> while a sleeping lock is acquired. It is used at the begin of the wait
> loop with TASK_UNINTERRUPTIBLE and while leaving it and restoring the
> original state. The latter part triggers the warning.
> 
> Drop the special state check. This is only used within the sleeping lock
> implementation and the assignment happens while the PI lock is held.
> While at it, drop set_current_state_no_track() because it has no users.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  include/linux/sched.h | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index a0c1c0cae992..b20264e17b02 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -132,16 +132,9 @@ struct task_group;
>  
>  #define __set_current_state_no_track(state_value)		\
>  	do {							\
> -		WARN_ON_ONCE(is_special_task_state(state_value));\
>  		current->state = (state_value);			\
>  	} while (0)

I don't think we need to keep the do { } while with a single line. It
is now equivalent to the non-debug version of __set_current_state()
which is defined as:

#define __set_current_state(state_value)				\
	current->state = (state_value)

-- Steve

>  
> -#define set_current_state_no_track(state_value)			\
> -	do {							\
> -		WARN_ON_ONCE(is_special_task_state(state_value));\
> -		smp_store_mb(current->state, (state_value));	\
> -	} while (0)
> -
>  #define set_special_state(state_value)					\
>  	do {								\
>  		unsigned long flags; /* may shadow */			\
> @@ -196,7 +189,6 @@ struct task_group;
>  	smp_store_mb(current->state, (state_value))
>  
>  #define __set_current_state_no_track(state_value)	__set_current_state(state_value)
> -#define set_current_state_no_track(state_value)		set_current_state(state_value)
>  
>  /*
>   * set_special_state() should be used for those states when the blocking task