linux-kernel - [PATCH] Fix the spurious unlock_cpu

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Message-ID: <20061103060427.GA12399@in.ibm.com>
Date:	Fri, 3 Nov 2006 11:34:27 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	torvalds@...l.org, akpm@...l.org
Cc:	linux-kernel@...r.kernel.org, martin@...enz.eu.org,
	srinivasa@...ibm.com, vatsa@...ibm.com
Subject: [PATCH] Fix the spurious unlock_cpu_hotplug false warnings.

Cpu-hotplug locking has a minor race case caused because of setting the
variable "recursive" to NULL *after* releasing the cpu_bitmask_lock in the
function unlock_cpu_hotplug,instead of doing so before releasing the
cpu_bitmask_lock. 

This was the cause of most of the recent false spurious lock_cpu_unlock
warnings.

This should fix the problem reported by Martin Lorenz reported in
http://lkml.org/lkml/2006/10/29/127.

Thanks to Srinivasa DS for pointing it out.

Signed-off-by: Gautham R Shenoy <ego@...ibm.com>

--
 kernel/cpu.c |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

Index: hotplug/kernel/cpu.c
===================================================================
--- hotplug.orig/kernel/cpu.c
+++ hotplug/kernel/cpu.c
@@ -58,8 +58,8 @@ void unlock_cpu_hotplug(void)
 		recursive_depth--;
 		return;
 	}
-	mutex_unlock(&cpu_bitmask_lock);
 	recursive = NULL;
+	mutex_unlock(&cpu_bitmask_lock);
 }
 EXPORT_SYMBOL_GPL(unlock_cpu_hotplug);
 
-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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