linux-kernel - Re: schedule() && prev/current (Was: [PATCH 3/3] Make get_current() __attribute_

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Message-ID: <1274250079.5605.9967.camel@twins>
Date:	Wed, 19 May 2010 08:21:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	David Howells <dhowells@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Yong Zhang <yong.zhang0@...il.com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: schedule() && prev/current (Was: [PATCH 3/3] Make
 get_current() __attribute__((const)))

On Tue, 2010-05-18 at 23:22 +0200, Oleg Nesterov wrote:

> And, looking at this patch I think that schedule() can be simplified
> a little bit.
> 
> "sched: Reassign prev and switch_count when reacquire_kernel_lock() fail"
> commit 6d558c3ac9b6508d26fd5cadccce51fc9d726b1c says:
> 
> 	Assume A->B schedule is processing,
> 	...
> 	Then on B's context,
> 	...
> 	prev and switch_count are related to A
> 
> How so? switch_count - yes, we should change it. But prev must be
> equal to B, and it must be equal to current. When we return from
> switch_to() registers/stack should be restored correctly, so we
> can do

What if schedule() got called at a different stack depth than we are
now?

I don't think we can assume anything about the stack context we just
switched to.
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