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

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Date:	Sat, 6 Jan 2007 20:13:21 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...l.org>
Cc:	vatsa@...ibm.com, Oleg Nesterov <oleg@...sign.ru>,
	David Howells <dhowells@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	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


* Andrew Morton <akpm@...l.org> wrote:

> > 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?

yes, yes, yes - lets please do that! The process freezer is already used 
for suspend, for hibernate and recently for kprobes - so its performance 
and robustness is being relied on and verified from multiple angles. I 
can see no reason why it couldnt be made really fast even on large 
boxes, if the need arises. (but even the current one is fast enough for 
any human-driven CPU hotplug stuff)

	Ingo
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