Re: [PATCH] fix-flush_workqueue-vs-cpu_dead-race-update

[Andrew Morton]

On Sat, 6 Jan 2007 22:08:51 +0530
Srivatsa Vaddagiri <vatsa@xxxxxxxxxx> 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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