linux-kernel - Re: [PATCH] wait: fix false timeouts when using wait_event

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Date:	Wed, 5 Jun 2013 18:45:07 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Imre Deak <imre.deak@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dave Jones <davej@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Jens Axboe <axboe@...nel.dk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Lukas Czerner <lczerner@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] wait: fix false timeouts when using wait_event_timeout()

Hello, Oleg.

On Wed, Jun 05, 2013 at 09:07:23PM +0200, Oleg Nesterov wrote:
> And in fact, perhaps we can implement wait_event_common() and avoid the
> code duplications?
> 
> 	#define __wait_no_timeout(timeout)	\
> 		(__builtin_constant_p(timeout) && (timeout) == MAX_SCHEDULE_TIMEOUT)
> 
> 	/* uglified signal_pending_state() */
> 	#define __wait_signal_pending(state)					\
> 		((state == TASK_INTERRUPTIBLE) ? signal_pending(current) :	\
> 		 (state == TASK_KILLABLE) ? fatal_signal_pending(current) :	\
> 		  0)
> 
> 	#define __wait_event_common(wq, condition, state, tout)			\
> 	({									\
> 		DEFINE_WAIT(__wait);						\
> 		long __ret = 0, __tout = tout;					\
> 										\
> 		for (;;) {							\
> 			prepare_to_wait(&wq, &__wait, state);			\
> 			if (condition) {					\
> 				__ret = __wait_no_timeout(tout) ?: __tout ?: 1;	\
> 				break;						\
> 			}							\
> 										\
> 			if (__wait_signal_pending(state)) {			\
> 				__ret = -ERESTARTSYS;				\
> 				break;						\
> 			}							\
> 										\
> 			if (__wait_no_timeout(tout))				\
> 				schedule();					\
> 			else if (__tout)					\
> 				__tout = schedule_timeout(__tout);		\
> 			else							\
> 				break;						\
> 		}								\
> 		finish_wait(&wq, &__wait);					\
> 		__ret;								\
> 	})

Heh, yeah, this looks good to me and a lot better than trying to do
the same thing over and over again and ending up with subtle
differences.

> Hmm. I compiled the kernel with the patch below,
> 
> 		$ size vmlinux
> 		   text	   data	    bss	    dec	    hex	filename
> 	-	4978601	2935080	10104832	18018513	112f0d1	vmlinux
> 	+	4977769	2930984	10104832	18013585	112dd91	vmlinux

Nice.  Provided you went over assembly outputs of at least some
combinations, please feel free to add

 Reviewed-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun
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