linux-kernel - Re: [PATCH 0/6] sched, wait: Collapse __wait

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Date:	Tue, 1 Oct 2013 16:09:40 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] sched, wait: Collapse __wait_event macros -v4

On 09/30, Oleg Nesterov wrote:
>
> On 09/30, Peter Zijlstra wrote:
> >
> > On Mon, Sep 30, 2013 at 07:40:54PM +0200, Oleg Nesterov wrote:
> > > Once again, of course I do not blame this series, but
> > > wait_event_timeout(wq, true, 0) still returns 0.
> >
> > So we have:
> >
> > [...snip...]
>
> > So wait_event_timeout(wq, true, 0) turns into:
>
> Not really, because of fast-path check,
>
> 	#define wait_event_timeout(wq, condition, timeout)			\
> 	({									\
> 		long __ret = timeout;						\
> 		if (!(condition)) 						\
> 			__ret = __wait_event_timeout(wq, condition, timeout);	\
> 		__ret;								\
> 	})
>
> we do not even call __wait_event_timeout() if "condition" is already
> true at the start.

But somehow I didn't realize that ___wait_cond_timeout() can be used
as is, so the simple patch below should work?

Oleg.

--- x/include/linux/wait.h
+++ x/include/linux/wait.h
@@ -270,7 +270,7 @@ do {									\
 #define wait_event_timeout(wq, condition, timeout)			\
 ({									\
 	long __ret = timeout;						\
-	if (!(condition)) 						\
+	if (!___wait_cond_timeout(condition)) 				\
 		__ret = __wait_event_timeout(wq, condition, timeout);	\
 	__ret;								\
 })
@@ -328,7 +328,7 @@ do {									\
 #define wait_event_interruptible_timeout(wq, condition, timeout)	\
 ({									\
 	long __ret = timeout;						\
-	if (!(condition))						\
+	if (!___wait_cond_timeout(condition))				\
 		__ret = __wait_event_interruptible_timeout(wq, 		\
 						condition, timeout);	\
 	__ret;								\
@@ -770,7 +770,7 @@ do {									\
 						  timeout)		\
 ({									\
 	long __ret = timeout;						\
-	if (!(condition))						\
+	if (!___wait_cond_timeout(condition))				\
 		__ret = __wait_event_interruptible_lock_irq_timeout(	\
 					wq, condition, lock, timeout);	\
 	__ret;								\

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