linux-kernel - Re: [PATCH] fix-flush_workqueue-vs-cpu

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Message-ID: <20070106163851.GA13579@in.ibm.com>
Date:	Sat, 6 Jan 2007 22:08:51 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...l.org>, David Howells <dhowells@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...l.org>,
	linux-kernel@...r.kernel.org, Gautham shenoy <ego@...ibm.com>
Subject: Re: [PATCH] fix-flush_workqueue-vs-cpu_dead-race-update

On Sat, Jan 06, 2007 at 07:30:35PM +0300, Oleg Nesterov wrote:
> Stupid me. Thanks.
> 
> I'll try to do something else tomorrow. Do you see a simple soulution?

Sigh ..I dont see a simple solution, unless we have something like
lock_cpu_hotplug() ..

Andrew,
	This workqueue problem has exposed a classic example of how 
tough/miserable it can be to write hotplug safe code w/o something like
lock_cpu_hotplug() ..Are you still inclined towards banning it? :)

FYI, the lock_cpu_hotplug() rewrite proposed by Gautham at
http://lkml.org/lkml/2006/10/26/65 may still need refinement to avoid
all the kind of deadlocks we have unearthed with workqueue example. I
can review that design with Gautham if there is some interest to
revive lock_cpu_hotplug() ..

> The current usage of workqueue_mutex (I mean stable kernel) is broken
> and deadlockable. We really need to change it.

Yep ..

-- 
Regards,
vatsa
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