linux-kernel - Re: [PATCH 6/7 linux-next] wan: cosa: replace current->state by set_current

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Date:	Fri, 20 Feb 2015 11:31:53 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Fabian Frederick <fabf@...net.be>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Jan \"Yenya\" Kasprzak" <kas@...muni.cz>, netdev@...r.kernel.org
Subject: Re: [PATCH 6/7 linux-next] wan: cosa: replace current->state by
 set_current_state()

On Fri, 2015-02-20 at 19:58 +0100, Peter Zijlstra wrote:
> On Fri, Feb 20, 2015 at 09:34:28PM +0300, Sergei Shtylyov wrote:
> > Hello.
> > 
> > On 02/20/2015 09:12 PM, Fabian Frederick wrote:
> > 
> > >Use helper functions to access current->state.
> > >Direct assignments are prone to races and therefore buggy.
> > 
> > >current->state = TASK_RUNNING is replaced by __set_current_state()
> > 
> >    You sometimes use __set_current_state() and sometimes set_current_state().
> 
> It depends on which state; setting yourself TASK_RUNNING is free of
> wakeup races -- you're already running after all, so it can safely use
> __set_current_state().

Maybe this might be self documented in set_current_state(),
as we have about 120 calls to __set_current_state(TASK_RUNNING)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 41c60e5302d7..26133da6445e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -275,7 +275,11 @@ extern char ___assert_task_state[1 - 2*!!(
 #define set_current_state(state_value)				\
 	do {							\
 		current->task_state_change = _THIS_IP_;		\
-		set_mb(current->state, (state_value));		\
+		if (__builtin_constant_p(state_value) &&	\
+		    (state_value) == TASK_RUNNING)		\
+			current->state = (state_value);		\
+		else						\
+			set_mb(current->state, (state_value));	\
 	} while (0)
 
 #else



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