linux-kernel - Re: [PATCH]:Replacing current->state with set_current

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Message-ID: <alpine.LFD.0.98.0704250843300.9964@woody.linux-foundation.org>
Date:	Wed, 25 Apr 2007 08:45:51 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	Shani Moideen <shani.moideen@...ro.com>,
	linux-kernel@...r.kernel.org, kernel-janitors@...ts.osdl.org
Subject: Re: [PATCH]:Replacing current->state with set_current_state in
 kernel/signal.c



On Wed, 25 Apr 2007, Eric Dumazet wrote:
> 
> Either you think you corrected a BUG, so please state it clearly in 
> Changelog so that Linus immediatly apply your patch for 2.6.21 :)

It's not a bug.

Setting current state manually is fine _iff_ you don't actually test a 
condition value. It's only if you do

	/* This has a race, and is bad! */
	current->state = TASK_INTERRUPTIBLE;
	if (some_condition)
		schedule();

that you have a race: the CPU (or the compiler, for that matter) can move 
the "some_condition" check up to before setting TASK_INTERRUPTIBLE, and if 
another CPU comes in and wakes you up, you might lose the wakeup.

But doing

	/* This is fine */
	current->state = TASK_INTERRUPTIBLE;
	schedule();

is fine.

		Linus
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