linux-kernel - Re: [PATCH 3/3] locking: rtmutex: set state back to running on error

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Date:	Sun, 01 Mar 2015 06:35:28 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Maarten Lankhorst <maarten.lankhorst@...onical.com>
Subject: Re: [PATCH 3/3] locking: rtmutex: set state back to running on error

On Fri, 2015-02-27 at 17:57 +0100, Sebastian Andrzej Siewior wrote:
> The "usual" path is:
> - rt_mutex_slowlock()
>  - set_current_state()
>  - task_blocks_on_rt_mutex() (ret 0)
>  - __rt_mutex_slowlock()
>    - sleep or not but do return with __set_current_state(TASK_RUNNING)
>  - back to caller.
> 
> In the early error case where task_blocks_on_rt_mutex() return -EDEADLK
> we never change the task's state back to RUNNING. I assume this is
> intended. Without this change after ww_mutex using rt_mutex the selftest
> passes but later I get plenty of
> | bad: scheduling from the idle thread!
> backtraces.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  kernel/locking/rtmutex.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 6d7d72ffa619..c4d07f254bb4 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -1305,6 +1305,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
>  	}
>  
>  	if (unlikely(ret)) {
> +		set_current_state(TASK_RUNNING);
>  		if (rt_mutex_has_waiters(lock))
>  			remove_waiter(lock, &waiter);
>  		/* ww_mutex need the error reported */

This may want a Fixes: afffc6c1 tag, and should use the double
underscore variant methinks.

	-Mike

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