linux-kernel - Re: [PATCH 2/3] mm/page_alloc: convert zone_pcp_update() to use on_each_cpu() instead of stop

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Message-ID: <51637470.5030906@linux.vnet.ibm.com>
Date:	Mon, 08 Apr 2013 18:52:48 -0700
From:	Cody P Schafer <cody@...ux.vnet.ibm.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] mm/page_alloc: convert zone_pcp_update() to use on_each_cpu()
 instead of stop_machine()

On 04/08/2013 03:18 PM, KOSAKI Motohiro wrote:
> (4/8/13 3:49 PM), Cody P Schafer wrote:>
>> If this turns out to be an issue, schedule_on_each_cpu() could be an
>> alternative.
>
> no way. schedule_on_each_cpu() is more problematic and it should be removed
> in the future.
> schedule_on_each_cpu() can only be used when caller task don't have any lock.
> otherwise it may make deadlock.

I wasn't aware of that. Just to be clear, the deadlock you're referring 
to isn't the same one refered to in

commit b71ab8c2025caef8db719aa41af0ed735dc543cd
Author: Tejun Heo <tj@...nel.org>
Date:   Tue Jun 29 10:07:14 2010 +0200
workqueue: increase max_active of keventd and kill current_is_keventd()

and

commit 65a64464349883891e21e74af16c05d6e1eeb4e9
Author: Andi Kleen <ak@...ux.intel.com>
Date:   Wed Oct 14 06:22:47 2009 +0200
HWPOISON: Allow schedule_on_each_cpu() from keventd

If you're referencing some other deadlock, could you please provide a 
link to the relevant discussion? (I'd really like to add a note to 
schedule_on_each_cpu()'s doc comment about it so others can avoid that 
pitfall).

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