From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Subject: Re: [RFC PATCH 0/3] restartable sequences v2: fast user-space percpu
 critical sections
Date: Fri, 8 Apr 2016 13:02:32 +0200
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Cc: Mathieu Desnoyers <mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>, "Paul E. McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Paul Turner <commonly-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Andi Kleen <andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org>, Chris Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>, Dave Watson <davejwatson-b10kYP2dOMg@public.gmane.org>, Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>, Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Andrew Hunter <ahh-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
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On Thu, Apr 07, 2016 at 03:05:26PM -0700, Andy Lutomirski wrote:

> It doesn't, which is what I like about my variant.  If the thread
> accesses the protected data structure, though, it should bump the
> sequence count, which will cause the first thread to about when it
> gets scheduled in.

Nope it won't, because that first thread is right at the commit
instruction, nothing will stop it from executing that store and clobbing
what we just wrote.

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Date: Fri, 8 Apr 2016 13:02:32 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.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
Message-ID: <20160408110232.GP3448@twins.programming.kicks-ass.net>
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On Thu, Apr 07, 2016 at 03:05:26PM -0700, Andy Lutomirski wrote:

> It doesn't, which is what I like about my variant.  If the thread
> accesses the protected data structure, though, it should bump the
> sequence count, which will cause the first thread to about when it
> gets scheduled in.

Nope it won't, because that first thread is right at the commit
instruction, nothing will stop it from executing that store and clobbing
what we just wrote.