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Subject: Re: Change in functionality of futex() system call.
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Oliver <david@rgmadvisors.com>, linux-kernel@vger.kernel.org,
        Shawn Bohrer <sbohrer@rgmadvisors.com>,
        Zachary Vonler <zvonler@rgmadvisors.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Hugh Dickins <hughd@google.com>, Thomas Gleixner <tglx@linutronix.de>,
        Darren Hart <dvhart@linux.intel.com>, Ingo Molnar <mingo@elte.hu>
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Date: Mon, 06 Jun 2011 19:11:37 +0200
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Le lundi 06 juin 2011 à 19:05 +0200, Peter Zijlstra a écrit :

> Dunno, using futexes on private file maps is stupid imo, its just asking
> for trouble, ro private file maps are even worse. Forcing the COW is the
> only sane answer in that it gives consistent results and 'breaks' silly
> expectations early instead of sometimes.
> 
> Anyway, that's not really the issue here, as David uses MAP_SHARED (as
> one should if one is interested in the shared value).

Sure, but maybe another guy is 'stupid' and uses MAP_PRIVATE on its
read-only mappings. With old kernels this was working, and we were not
doing the COW.

(Note : the other process writes to the file, using MAP_SHARED)


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