linux-kernel - Re: 2.6.26-rt1

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Date:	Fri, 1 Aug 2008 14:11:17 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Jürgen Mell <j.mell@...nline.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>,
	Clark Williams <williams@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Carsten Emde <ce@...g.ch>
Subject: Re: 2.6.26-rt1

On Wed, Jul 30, 2008 at 11:01:32AM +0200, Jürgen Mell wrote:
> Hello Thomas,
> 
> On Wednesday, 30. July 2008, Thomas Gleixner wrote:
> > We are pleased to announce the 2.6.26-rt1 tree, which can be
> > downloaded from the location:
> 
> I have tried the new kernel and have some good news and some bad news:
> 
> The good news: The machine boots and seems to run without major problems.
> 
> The bad news: It produces continuously lots of bug messages in the error 
> logs (cf. attached dmesg.tgz). The error at rtmutex.c:743 was already 
> present in 2.6.25-rt* when ACPI was enabled. The 'using smp_processor_id 
> ()  in preemptible code' is new here with 2.6.26.
> 
> Machine is an old Athlon XP (single core) on an EPOX mainboard with VIA 
> chipset.
> 
> If I can help with testing, please let me know.

The following patch should clear things up.  It is against 2.6.25.8-rt7,
but should still apply.

------------------------------------------------------------------------

Disable preemption around statistics for RCU boost and unboost calls.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---

 rcupreempt-boost.c |   20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff -urpNa -X dontdiff linux-2.6.25.8-rt7/kernel/rcupreempt-boost.c linux-2.6.25.8-rt7-preemptfix/kernel/rcupreempt-boost.c
--- linux-2.6.25.8-rt7/kernel/rcupreempt-boost.c	2008-06-24 14:14:52.000000000 -0700
+++ linux-2.6.25.8-rt7-preemptfix/kernel/rcupreempt-boost.c	2008-06-24 14:38:59.000000000 -0700
@@ -205,11 +205,23 @@ RCU_BOOST_TRACE_FUNC_DECL(boost_readers)
 RCU_BOOST_TRACE_FUNC_DECL(try_unboost_readers)
 RCU_BOOST_TRACE_FUNC_DECL(unboost_readers)
 RCU_BOOST_TRACE_FUNC_DECL(over_taken)
+static void rcu_trace_boost_boost_called_preempt(void)
+{
+	preempt_disable();
+	rcu_trace_boost_boost_called(RCU_BOOST_ME);
+	preempt_enable();
+}
+static void rcu_trace_boost_unboost_called_preempt(void)
+{
+	preempt_disable();
+	rcu_trace_boost_unboost_called(RCU_BOOST_ME);
+	preempt_enable();
+}
 #else /* CONFIG_RCU_TRACE */
 /* These were created by the above macro "RCU_BOOST_TRACE_FUNC_DECL" */
-# define rcu_trace_boost_task_boost_called(rbd) do { } while (0)
+# define rcu_trace_boost_task_boost_called_preempt(rbd) do { } while (0)
 # define rcu_trace_boost_task_boosted(rbd) do { } while (0)
-# define rcu_trace_boost_boost_called(rbd) do { } while (0)
+# define rcu_trace_boost_boost_called_preempt(rbd) do { } while (0)
 # define rcu_trace_boost_try_boost(rbd) do { } while (0)
 # define rcu_trace_boost_boosted(rbd) do { } while (0)
 # define rcu_trace_boost_unboost_called(rbd) do { } while (0)
@@ -261,7 +273,7 @@ void __rcu_preempt_boost(void)
 
 	WARN_ON(!current->rcu_read_lock_nesting);
 
-	rcu_trace_boost_boost_called(RCU_BOOST_ME);
+	rcu_trace_boost_boost_called_preempt();
 
 	/* check to see if we are already boosted */
 	if (unlikely(rcu_is_boosted(curr)))
@@ -313,7 +325,7 @@ void __rcu_preempt_unboost(void)
 	int prio;
 	unsigned long flags;
 
-	rcu_trace_boost_unboost_called(RCU_BOOST_ME);
+	rcu_trace_boost_unboost_called_preempt();
 
 	/* if not boosted, then ignore */
 	if (likely(!rcu_is_boosted(curr)))

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