linux-kernel - Re: [PATCH 0/3] state/exit_state cleanups (Was: Remove unused variable ret from sync_thread

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Message-ID: <20131113144856.GL26898@twins.programming.kicks-ass.net>
Date:	Wed, 13 Nov 2013 15:48:56 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Laight <David.Laight@...LAB.COM>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Ingo Molnar <mingo@...nel.org>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] state/exit_state cleanups (Was: Remove unused
 variable ret from sync_thread_master())

On Wed, Nov 13, 2013 at 03:35:52PM +0100, Oleg Nesterov wrote:
> On 11/12, Oleg Nesterov wrote:
> >
> > On 11/12, Peter Zijlstra wrote:
> > >
> > > We have to put in something...
> > >
> > > 	BUILD_BUG_ON(1 + ilog2(TASK_STATE_MAX) != ARRAY_SIZE(task_state_array));
> > >
> > > However, since we always set it together with TASK_UNINTERUPTIBLE
> > > userspace shouldn't actually ever see the I thing.
> >
> > OOPS. I didn't know that get_task_state() does &= TASK_REPORT. So it
> > can never report anything > EXIT_DEAD.
> >
> > Perhaps we should change BUILD_BUG_ON() and shrink task_state_array?
> 
> Seriously, imho this looks confusing enough and deserves a cleanup.
> 
> 
> As for "nobody should use exit_state". I'll try to recheck, but iirc
> we already discussed this... do you remember any reason why
> schedule_debug() can't check prev->state == TASK_DEAD instead of
> ->exit_state?

I have no such memories :/ but a quick test shows that such a kernel
does boot without issue.

> Note that ->exit_state is not exactly right, it is set by exit_notify()
> but in_atomic_preempt_off() should be only ignored when the task does
> the last schedule() in TASK_DEAD.

Agreed.

For these patches:

Acked-by: Peter Zijlstra <peterz@...radead.org>
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