Date: Sat, 9 Apr 2005 09:07:38 +0200
From: Ingo Molnar <mingo@elte.hu>
To: davidm@hpl.hp.com
Cc: "Luck, Tony" <tony.luck@intel.com>, linux-kernel@vger.kernel.org
Subject: Re: [patch] sched: unlocked context-switches
Message-ID: <20050409070738.GA5444@elte.hu>
References: <3R6Ir-89Y-23@gated-at.bofh.it> <ugoecowjci.fsf@panda.mostang.com>
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* David Mosberger-Tang <David.Mosberger@acm.org> wrote:

>  > The ia64_switch_to() code includes a section that can change a
>  > pinned MMU mapping (when the stack for the new process is in a
>  > different granule from the stack for the old process).  The code
>  > beyond the ".map" label in arch/ia64/kernel/entry.S includes the
>  > comment:
> 
> Also, there was a nasty dead-lock that could trigger if the 
> context-switch was interrupted by a TLB flush IPI.  I don't remember 
> the details offhand, but I'm pretty sure it had to do with 
> switch_mm(), so I suspect it may not be enough to disable irqs just 
> for ia64_switch_to().  Tread with care!

we'll see. The patch certainly needs more testing. Generally we do 
switch_mm()'s outside of the scheduler as well, without disabling 
interrupts.

	Ingo
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