Date: Tue, 12 Apr 2005 08:42:53 +0200
From: Ingo Molnar <mingo@elte.hu>
To: davidm@hpl.hp.com
Cc: "David S. Miller" <davem@davemloft.net>, tony.luck@intel.com,
       linux-kernel@vger.kernel.org
Subject: Re: [patch] sched: unlocked context-switches
Message-ID: <20050412064253.GA1289@elte.hu>
References: <3R6Ir-89Y-23@gated-at.bofh.it> <ugoecowjci.fsf@panda.mostang.com> <20050409070738.GA5444@elte.hu> <16983.33049.962002.335198@napali.hpl.hp.com> <20050409155810.593d8f7b.davem@davemloft.net> <20050410064324.GA24596@elte.hu> <16987.7956.806699.617633@napali.hpl.hp.com>
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* David Mosberger <davidm@napali.hpl.hp.com> wrote:

> Now, Ingo says that the order is reversed with his patch, i.e., 
> switch_mm() happens after switch_to().  That means flush_tlb_mm() may 
> now see a current->active_mm which hasn't really been activated yet.  
> That should be OK since it would just mean that we'd do an early (and 
> duplicate) activate_context().  While it does not give me a warm and 
> fuzzy feeling to have this inconsistent state be observable by 
> interrupt-handlers (and, in particular, IPI-handlers), I don't see any 
> problem with it off hand.

thanks for the analysis. I fundamentally dont have any fuzzy feeling 
from having _any_ portion of the context-switch path nonatomic, but with 
more complex hardware it's just not possible it seems.

	Ingo
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