linux-kernel - Re: [REGRESSION][PATCH] mqueue: Ignore the validity of abs_timeout parameter when message can be performed immediately

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Date:	Wed, 14 Mar 2012 23:08:53 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Akira Takeuchi <takeuchi.akr@...panasonic.com>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	Carsten Emde <C.Emde@...dl.org>,
	Manfred Spraul <manfred@...orfullife.com>
Subject: Re: [REGRESSION][PATCH] mqueue: Ignore the validity of abs_timeout
 parameter when message can be performed immediately

On Wed, 14 Mar 2012, Andrew Morton wrote:

> On Fri, 02 Mar 2012 16:42:35 +0900
> Akira Takeuchi <takeuchi.akr@...panasonic.com> wrote:
> 
> > This patch fixes up the regression problem of mq_timed{send,receive} syscall.
> > 
> > When a message of mqueue can be performed immediately,
> > the validity of abs_timeout parameter should not be checked.
> > 
> > According to the manpage of mq_timedreceive:
> >     Under no circumstance shall the operation fail with a timeout
> >     if a message can be removed from the message queue immediately.
> >     The validity of the abstime parameter need not be checked
> >     if a message can be removed from the message queue immediately.

Those POSIX spec folks definitely have a seriously distorted
relationship to timers and timekeeping.

So the caller knows upfront when he needs to provide a valid timespec
and when not. So the users of mq_.... are into crystal ball
programming or what?

> > On 2.6.35+ kernel, mq_timed{send,receive} returns EINVAL incorrectly,
> > in this situation.
> > 
> > I found this problem during the OPTS testcase
> > "conformance/interfaces/mq_timedreceive/10-2":
> > 
> >     # ./10-2.test
> >     FAIL: the validity of abs_timeout is checked
> >     Test FAILED
> 
> Are you able to identify the commit which caused this regression?  I'm
> guessing
> 
> commit 9ca7d8e6834c40a99622bbe4a88aaf64313ae43c
> Author:     Carsten Emde <C.Emde@...dl.org>
> AuthorDate: Fri Apr 2 22:40:20 2010 +0200
> Commit:     Thomas Gleixner <tglx@...utronix.de>
> CommitDate: Tue Apr 6 21:50:03 2010 +0200
> 
>     mqueue: Convert message queue timeout to use hrtimers                       

Right, because nobody imagined that the specification would be as
asinine.

I'll pick it up and add a stable tag.

Sigh,

	tglx
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