linux-kernel - Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

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Message-ID: <480F4BD9.8090003@rtr.ca>
Date:	Wed, 23 Apr 2008 10:46:49 -0400
From:	Mark Lord <lkml@....ca>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	npiggin@...e.de, torvalds@...ux-foundation.org
Subject: Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

Jens Axboe wrote:
> On Wed, Apr 23 2008, Mark Lord wrote:
>..
>> The second bug, is that for the halt case at least,
>> nobody waits for the other CPU to actually halt
>> before continuing.. so we sometimes enter the shutdown
>> code while other CPUs are still active.
>>
>> This causes some machines to hang at shutdown,
>> unless CPU_HOTPLUG is configured and takes them offline
>> before we get here.
> 
> I'm guessing there's a reason it doesn't pass '1' as the last argument,
> because that would fix that issue?
..

Undoubtedly -- perhaps the called CPU halts, and therefore cannot reply.  :)

But some kind of pre-halt ack, perhaps plus a short delay by the caller
after receipt of the ack, would probably suffice to kill that bug.

But I really haven't studied this code enough to know,
other than that it historically has been a sticky area
to poke around in.

Cheers
 

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