linux-kernel - Re: 2.6.31.4-rt14 posix message queues problem

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Message-ID: <alpine.LFD.2.00.0910152105430.8932@localhost.localdomain>
Date:	Thu, 15 Oct 2009 21:09:32 +0200 (CEST)
From:	John Kacur <jkacur@...hat.com>
To:	Joerg.Abraham@...atel-lucent.de, linux-kernel@...r.kernel.org
cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>
Subject: Re: 2.6.31.4-rt14 posix message queues problem


> From: Joerg Abraham <Joerg.Abraham@...atel-lucent.de>
> Date: Thu, Oct 15, 2009 at 7:51 PM
> Subject: 2.6.31.4-rt14 posix message queues problem
> To: LKML <linux-kernel@...r.kernel.org>
> 
> 
> Hi,
> 
> During some performance measurement I stumbled over unexpected bad
> results for a posix message queue test case. Which is not surprising
> since the kernel log shows a "BUG: scheduling while atomic:" on every
> measurement trigger.
> 
> Attached is the kernel log for an embedded 8572ds powerpc system and a
> condensed user space test appli. The test appli uses 2 processes
> (mq_server and mq_client) and pingpongs some messages via posix
> message queues. Please see the c-file header for details (the appli
> itself makes not much sense but shows the problem).
> 
> ./mq_server
> ./mq_client # just crashes during run
> 
> The problem does _not_ occur on kernels 2.6.29.6-rt24, 2.6.29.6
> vanilla and 2.6.31.4 vanilla. The problem does _also_ show up on an
> embedded x86_64 system and a full featured fc11 x86_64 system running
> a 2.6.31.4-rt14 based kernel, so I dont think it's arch dependent.
> 
> Can anybody reproduce the crash ???
> 
> If you need more info's please let me know.
> 
> [And if I'm doing stupid things just forgive me]
> 
> Thanx
> 
> Joerg

Hello Joerg

Does the following patch solve your problem? 

>From 69fde4357db4a054733cbca4158606160e821a3a Mon Sep 17 00:00:00 2001
From: John Kacur <jkacur@...hat.com>
Date: Thu, 15 Oct 2009 20:52:37 +0200
Subject: [PATCH] preempt_disable_rt(); should be paired with preempt_enable_rt()

Signed-off-by: John Kacur <jkacur@...hat.com>
---
 ipc/mqueue.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 63a47f7..ab4df36 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -830,7 +830,7 @@ static inline void pipelined_send(struct mqueue_inode_info *info,
 	wake_up_process(receiver->task);
 	smp_wmb();
 	receiver->state = STATE_READY;
-	preempt_enable_nort();
+	preempt_enable_rt();
 }
 
 /* pipelined_receive() - if there is task waiting in sys_mq_timedsend()
-- 
1.6.0.6

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