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

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Message-Id: <20070106111117.54bb2307.akpm@osdl.org>
Date:	Sat, 6 Jan 2007 11:11:17 -0800
From:	Andrew Morton <akpm@...l.org>
To:	vatsa@...ibm.com
Cc:	Oleg Nesterov <oleg@...sign.ru>,
	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, 6 Jan 2007 22:08:51 +0530
Srivatsa Vaddagiri <vatsa@...ibm.com> wrote:

> 	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? :)

I don't ban stuff - I just advocate ;)

I would still prefer that we not try to invent a new magical lock,
but yes, the current approach is looking troublesome.

> 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() ..

Has anyone thought seriously about using the process freezer in the
cpu-down/cpu-up paths?  That way we don't need to lock anything anywhere?
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