linux-kernel - Re: [PATCH 6/6] ipc/sem.c: make semctl(,,{GETNCNT,GETZCNT}) standard compliant

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Date:	Tue, 20 May 2014 20:30:05 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Michael Kerrisk <mtk.manpages@...il.com>, 1vier1@....de
Subject: Re: [PATCH 6/6] ipc/sem.c: make semctl(,,{GETNCNT,GETZCNT}) standard
 compliant

Hi Andrew,

On 05/20/2014 12:46 AM, Andrew Morton wrote:
> On Sun, 18 May 2014 09:58:37 +0200 Manfred Spraul <manfred@...orfullife.com> wrote:
>
>> SUSv4 clearly defines how semncnt and semzcnt must be calculated:
>> A task waits on exactly one semaphore:
>> The semaphore from the first operation in the sop array that cannot proceed.
>>
>> The Linux implementation never followed the standard, it tried to count all
>> semaphores that might be the reason why a task sleeps.
>>
>> This patch fixes that.
> What are the back-compatibility implications of this change?
A really good question:
- there is no application in Fedora that uses GETNCNT or GETZCNT.
- application that use only single-sop semop() are also safe, the 
difference only affects complex apps.
- portable application are also safe, the new behavior is standard 
compliant.

But that's it. The old behavior existed in Linux from 0.99.something 
until now.

What about adding a WARN_ON_ONCE() if the case where the behavior 
differs happens?
Should I write a patch?

--
     Manfred
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