linux-kernel - Re: Regression with orderly

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Date:	Tue, 12 Mar 2013 11:42:13 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Lucas De Marchi <lucas.de.marchi@...il.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>, david@...son.dropbear.id.au,
	Kees Cook <keescook@...omium.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Feng Hong <hongfeng@...vell.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
Subject: Re: Regression with orderly_poweroff()

On Tue, Mar 12, 2013 at 11:22 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> And how this can help? The real problem is not GFP_KERNEL.
> call_usermodehelper_exec(UMH_WAIT_EXEC) will block.

Well, it's probably a starting point.

You need to do the argument handling atomically, because you cannot
delay that in a workqueue (the arguments will be long gone by the time
the workqueue starts up). So I think the fix is a combination of your
and Lucas' code, where you first do the setup atomically (copying the
arguments and allocating that space with GFP_ATOMIC) and then you do a
workqueue to actually do the real work of the usermode helper thing.

                 Linus
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