quoted

From: Joerg Abraham <redacted>
Date: Thu, Oct 15, 2009 at 7:51 PM
Subject: 2.6.31.4-rt14 posix message queues problem
To: LKML <redacted>


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