From: Peter Zijlstra <peterz@infradead.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Darren Hart <dvhart@linux.intel.com>,
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>, Ingo Molnar <mingo@elte.hu>
Subject: Re: Change in functionality of futex() system call.
Date: Thu, 09 Jun 2011 14:05:08 +0200 [thread overview]
Message-ID: <1307621108.3941.77.camel@twins> (raw)
In-Reply-To: <1307383898.3098.90.camel@edumazet-laptop>
On Mon, 2011-06-06 at 20:11 +0200, Eric Dumazet wrote:
> Now, what if other software uses a MAP_PRIVATE ro mapping ?
>
> It was working in previous kernels as well.
>
> We can say its stupid, but IMHO its not.
>
> In other words, this program should work, if process never touches
> (writes) into first page.
>
> This program on previous kernels gave :
> rc=-1 errno=11
> (allowing to wait for a value change and a futex_WAKE)
>
> With new kernel :
> rc=-1 errno=14 [ no sleep allowed ]
Yeah, so friggin what? I can write a similar program that is broken with
the old behaviour. The fact that the semantics are just crap (wtf does
it mean to FUTEX_WAIT on a address that changes mapping on COW) should
be enough to convince you that the old behaviour simply doesn't make
sense.
Once the COW happened you shouldn't be able to observe the old page, yet
that's exactly what the still pending FUTEX_WAIT will do.
The fact that this can happen, means the behaviour is broken, no if else
or buts about it.
next prev parent reply other threads:[~2011-06-09 12:05 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-06 14:28 Change in functionality of futex() system call David Oliver
2011-06-06 15:23 ` Eric Dumazet
2011-06-06 15:56 ` Shawn Bohrer
2011-06-06 16:11 ` Peter Zijlstra
2011-06-06 16:16 ` Peter Zijlstra
2011-06-06 16:22 ` Eric Dumazet
2011-06-06 16:29 ` Peter Zijlstra
2011-06-06 16:42 ` Eric Dumazet
2011-06-06 17:05 ` Peter Zijlstra
2011-06-06 17:11 ` Eric Dumazet
2011-06-06 17:27 ` Steven Rostedt
2011-06-06 17:56 ` Darren Hart
2011-06-06 18:23 ` Peter Zijlstra
2011-06-06 18:27 ` Eric Dumazet
2011-06-25 0:00 ` Darren Hart
2011-06-27 16:48 ` Shawn Bohrer
2011-06-06 17:53 ` Darren Hart
2011-06-06 18:11 ` Eric Dumazet
2011-06-07 3:13 ` Darren Hart
2011-06-07 3:49 ` Eric Dumazet
2011-06-07 14:44 ` Andy Lutomirski
2011-06-07 15:56 ` Darren Hart
2011-06-07 15:58 ` Eric Dumazet
2011-06-07 18:43 ` Andrew Lutomirski
2011-06-07 19:01 ` Darren Hart
2011-06-07 19:04 ` Andrew Lutomirski
2011-06-07 19:06 ` Eric Dumazet
2011-06-07 19:10 ` David Oliver
2011-06-07 19:19 ` Andrew Lutomirski
2011-06-07 19:33 ` David Oliver
2011-06-07 19:53 ` Andrew Lutomirski
2011-06-07 20:04 ` David Oliver
2011-06-07 20:12 ` Andrew Lutomirski
2011-06-07 22:26 ` Kyle Moffett
2011-06-08 15:20 ` David Oliver
2011-06-08 15:21 ` Andrew Lutomirski
2011-06-08 16:21 ` Darren Hart
2011-06-09 11:37 ` KOSAKI Motohiro
2011-06-09 12:05 ` Peter Zijlstra
2011-06-09 17:58 ` Peter Zijlstra
2011-06-10 3:30 ` KOSAKI Motohiro
2011-06-10 3:26 ` KOSAKI Motohiro
2011-06-07 18:30 ` Joel Becker
2011-06-09 12:05 ` Peter Zijlstra [this message]
2011-06-10 12:10 ` KOSAKI Motohiro
2011-06-10 17:29 ` Darren Hart
2011-06-13 2:11 ` KOSAKI Motohiro
2011-06-13 15:50 ` Darren Hart
2011-06-15 18:50 ` Shawn Bohrer
2011-06-15 18:54 ` Darren Hart
2011-06-17 13:40 ` Shawn Bohrer
2011-06-22 19:19 ` [PATCH RFC] futex: Fix regression with read only mappings Shawn Bohrer
2011-06-22 20:14 ` Darren Hart
2011-06-23 2:51 ` KOSAKI Motohiro
2011-06-23 15:26 ` Darren Hart
2011-06-23 19:49 ` Shawn Bohrer
2011-06-24 15:59 ` [PATCH v2] " Shawn Bohrer
2011-06-25 0:37 ` Darren Hart
2011-06-25 15:10 ` KOSAKI Motohiro
2011-06-27 16:40 ` Shawn Bohrer
2011-06-27 18:15 ` Peter Zijlstra
2011-06-27 20:41 ` Darren Hart
2011-06-27 21:08 ` Shawn Bohrer
2011-06-27 21:39 ` Darren Hart
2011-06-27 22:14 ` Shawn Bohrer
2011-06-27 23:17 ` Darren Hart
2011-06-27 22:22 ` [PATCH v3] " Shawn Bohrer
2011-06-28 10:54 ` Peter Zijlstra
2011-06-28 14:52 ` Darren Hart
2011-06-28 17:38 ` Shawn Bohrer
2011-06-28 20:58 ` Darren Hart
2011-06-28 23:55 ` Darren Hart
2011-06-29 14:56 ` Shawn Bohrer
2011-06-29 15:17 ` [PATCH v4] " Shawn Bohrer
2011-06-29 18:41 ` Darren Hart
2011-06-29 23:38 ` Thomas Gleixner
2011-06-30 4:19 ` Darren Hart
2011-06-30 14:02 ` David C. Oliver
2011-06-30 15:41 ` Darren Hart
2011-06-30 16:21 ` [PATCH v5] " Shawn Bohrer
2011-07-12 15:27 ` Shawn Bohrer
2011-07-25 15:20 ` Shawn Bohrer
2011-07-25 19:28 ` Thomas Gleixner
2011-07-26 19:04 ` [tip:core/urgent] " tip-bot for Shawn Bohrer
2011-06-28 10:50 ` [PATCH v2] " Peter Zijlstra
2011-06-28 14:19 ` Darren Hart
2011-06-28 14:23 ` Peter Zijlstra
2011-06-23 3:58 ` [PATCH RFC] " Shawn Bohrer
2011-06-23 3:23 ` Change in functionality of futex() system call KOSAKI Motohiro
-- strict thread matches above, loose matches on Subject: below --
2011-06-09 0:44 George Spelvin
2011-06-09 3:02 ` Darren Hart
2011-06-09 3:38 ` Andrew Lutomirski
2011-06-09 3:54 ` Eric Dumazet
2011-06-09 4:10 ` Andrew Lutomirski
2011-06-09 5:11 ` Eric Dumazet
2011-06-09 12:12 ` Andrew Lutomirski
2011-06-09 4:43 ` George Spelvin
2011-06-09 5:25 ` Eric Dumazet
2011-06-09 4:44 ` Kyle Moffett
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