linux-kernel - Re: [RFD] Freezing of kernel threads

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Message-ID: <alpine.LFD.0.98.0705121304390.3986@woody.linux-foundation.org>
Date:	Sat, 12 May 2007 13:11:34 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Gautham R Shenoy <ego@...ibm.com>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	Oleg Nesterov <oleg@...sign.ru>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFD] Freezing of kernel threads

On Sat, 12 May 2007, Linus Torvalds wrote:
> 
>  - make the rule be that you cannot sleep in the above macro, and make the 
>    rule be that CPU hotplug uses the same mechanisms that module unload 
>    already does!

Side note: we obviously already do the stop_machine_run thing for CPU 
down, so doing it for CPU bringup too would seem to just be a good thing. 
And it means that the locking for CPU's disappearing is the same as the 
locking rules for CPU's appearing: you just want to make sure to disable 
preemption (which you already have to do, to make the "CPU went away" case 
work out).

So how about just making sure "__cpu_up()" gets called with the same 
stop_machine_run() logic? Maybe it's not *quite* a one-liner change, but 
it should come fairly close...

		Linus
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