linux-kernel - Re: [PATCH/RFC] sched: Remove SYSTEM_RUNNING checks from cond

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Message-Id: <20090708141024.f8b581c5.akpm@linux-foundation.org>
Date:	Wed, 8 Jul 2009 14:10:24 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	a.p.zijlstra@...llo.nl, oleg@...hat.com, avorontsov@...mvista.com,
	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC] sched: Remove SYSTEM_RUNNING checks from
 cond_resched*()

> On Wed, 8 Jul 2009 09:12:30 -0700 (PDT) Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> That said, I do agree that maybe SYSTEM_RUNNING isn't the right check. 
> Testing that the scheduler is initialized may be the more correct one. I 
> think the SYSTEM_RUNNING one just comes from that being used for other 
> debug issues.

Agreed.  system_state is too general.

If we specifically want to know whether it is safe to call schedule() then
let's create a global boolean it_is_safe_to_call_schedule and test that,
rather than testing something which indirectly and unreliably implies "it
is safe to call schedule".  If that boolean already exists then no-brainer.

All that being said, I wonder if the netconsole code should be using
msleep(1) instead.  Spinning on cond_resched() is a bit rude.  But one
would have to verify that it is safe to call schedule() at this time, and
for the netconsole caller, this is dubious.
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