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Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups
From: Mike Galbraith <mgalbraith@suse.de>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
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        Markus Trippelsdorf <markus@trippelsdorf.de>
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Date: Tue, 26 Oct 2010 09:29:04 +0200
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On Tue, 2010-10-26 at 09:07 +0200, Mike Galbraith wrote:
> On Thu, 2010-10-21 at 18:29 +0200, Oleg Nesterov wrote:
> 
> > It is not clear to me why do we need rcu_read_lock() and how it can help.
> > The tty can go away right after dereferencing signal->tty.
> 
> Which was Marcus' crash.  Didn't happen here only because I didn't have
> CONFIG_PREEMPT set.
> 
> Changes since v2:
>   - drop  

Bumped mouse, message escaped.

Doesn't matter though, damn thing just blew up during enable/disable
plus hackbench stress test, despite holding a reference to the tty at
every place tty changes (under sighand lock), and moving the task with
that reference held.

CONFIG_PREEMPT is being a little S.O.B.

	-Mike