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Date: Thu, 7 Apr 2016 17:39:48 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC PATCH 0/3] restartable sequences v2: fast user-space percpu
 critical sections
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On Thu, Apr 07, 2016 at 05:24:32PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 07, 2016 at 07:35:26AM -0700, Andy Lutomirski wrote:
> > That way we could take an async signal, handle it, and resume, even in
> > the middle of a commit, without aborting.  Of course, if the signal
> > hander tried to access the same rseq-protected resource, it would bump
> > the event counter and cause an abort.
> 
> Ah, so what happens if the signal happens before the commit but after
> the load of the seqcount?
> 
> Then, even if the signal motifies the count, we'll not observe.

Ah, and the same is true for preemptions. Which is why all this was
preemption driven, and not migration driven.