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SubjectRe: 2.6.31.4-rt14 posix message queues problem

> From: Joerg Abraham <Joerg.Abraham@alcatel-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@vger.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@redhat.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@redhat.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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