From mboxrd@z Thu Jan  1 00:00:00 1970
From: Torvald Riegel <triegel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: futex(2) man page update help request
Date: Fri, 23 Jan 2015 19:19:05 +0100
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Cc: "Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, Carlos O'Donell <carlos-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>, Jakub Jelinek <jakub-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, lkml <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Davidlohr Bueso <davidlohr.bueso-VXdhtT5mjnY@public.gmane.org>, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>, Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>, Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Darren Hart <dvhart-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Anton Blanchard <anton-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>, Petr Baudis <pasky-AlSwsSmVLrQ@public.gmane.org>, Eric Dumazet <edumazet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, bill o gallmeister <bgallmeister-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Jan Kiszka <jan.kiszka-kv7WeFo6aLtBDgjK7y7TUQ@public.gmane.org>, Daniel Wagner <wagi-kQCPcA+X3s7YtjvyW6yDsg@public.gmane.org>, Rich Felker <dalias-8zAoT0mYgF4@public.gmane.org>
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On Fri, 2015-01-16 at 16:46 -0800, Darren Hart wrote:
> On 1/16/15, 12:54 PM, "Michael Kerrisk (man-pages)"
> <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> 
> >Color me stupid, but I can't see this in futex_requeue(). Where is that
> >check that is "independent of the requeue type (normal/pi)"?
> >
> >When I look through futex_requeue(), all the likely looking sources
> >of EINVAL are governed by a check on the 'requeue_pi' argument.
> 
> 
> Right, in the non-PI case, I believe there are valid use cases: move to
> the back of the FIFO, for example (OK, maybe the only example?).

But we never guarantee a futex is a FIFO, or do we?  If we don't, then
such a requeue could be implemented as a no-op by the kernel, which
would sort of invalidate the use case.

(And I guess we don't want to guarantee FIFO behavior for futexes.)


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