From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wu Zhangjin <wuzhangjin@gmail.com>
Subject: [BUG] 2.6.29.1-rt8, undefined reference to hrtimer_wait_for_timer
Date: Tue, 21 Apr 2009 09:47:40 +0800
Message-ID: <1240278460.27360.8.camel@falcon>
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Cc: LKML <linux-kernel@vger.kernel.org>,
	rt-users <linux-rt-users@vger.kernel.org>,
	Ingo Molnar <mingo@elte.hu>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Carsten Emde <ce@ceag.ch>,
	Clark Williams <williams@redhat.com>,
	Frank Rowand <frank.rowand@am.sony.com>,
	Robin Gareus <robin@gareus.org>,
	Gregory Haskins <ghaskins@novell.com>,
	Philippe Reynes <philippe.reynes@isismpp.fr>,
	Fernando Lopez-Lezcano <nando@ccrma.Stanford.EDU>,
	Will Schmidt <will_schmidt@vnet.ibm.com>,
	Darren Hart <dvhltc@us.ibm.com>, Jan Blunck <jblunck@suse.de>,
	Sven-Thorsten Dietrich <sdietrich@novell.com>
To: Thomas Gleixner <tglx@linutronix.de>
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when using patch-2.6.29.1-rt8 with CONFIG_PREEMPT_SOFTIRQS=y, but not
enable PREEMPT_RT, there will be an error when linking kernel:

undefined reference to hrtimer_wait_for_timer

I found that, hrtimer_wait_for_timer is only defined when PREEMPT_RT is
enabled, but in include/linux/hrtimer.h, the source code is like this:

#ifdef CONFIG_PREEMPT_SOFTIRQS
 extern void hrtimer_wait_for_timer(const struct hrtimer *timer);
#else
# define hrtimer_wait_for_timer(timer) do { cpu_relax(); } while (0)

a possible fix should be:

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 8bafa35..1c1cdf3 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -366,7 +366,7 @@ static inline int hrtimer_restart(struct hrtimer
*timer)
 }
 
 /* Softirq preemption could deadlock timer removal */
-#ifdef CONFIG_PREEMPT_SOFTIRQS
+#if defined(CONFIG_PREEMPT_SOFTIRQS) && defined(CONFIG_PREEMPT_RT)
   extern void hrtimer_wait_for_timer(const struct hrtimer *timer);
 #else
 # define hrtimer_wait_for_timer(timer) do { cpu_relax(); } while (0)

-- 
Wu Zhangjin
DSLab, Lanzhou University, China
www.lemote.com, Jiangsu Province, China