[PATCH]kprobes comment patch around kprobes lock functions

[Keshavamurthy Anil S <anil.s.keshavamurthy@intel.com>]

On Thu, Sep 01, 2005 at 02:09:38PM -0700, Andrew Morton wrote:
> Now, probably there's deep magic happening here and I'm wrong.  If so then
> please explain the code's magic via a comment patch so the question doesn't
> arise again, thanks.
> 

This is a comment patch around lock_kprobes() and unlock_kprobes() functions.

Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>

===================================================================
 kernel/kprobes.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+)

Index: linux-2.6.13-mm1/kernel/kprobes.c
===================================================================
--- linux-2.6.13-mm1.orig/kernel/kprobes.c
+++ linux-2.6.13-mm1/kernel/kprobes.c
@@ -157,9 +157,16 @@ void __kprobes lock_kprobes(void)
 {
 	unsigned long flags = 0;
 
+	/* Avoiding local interrupts to happen right after we take the kprobe_lock
+	 * and before we get a chance to update kprobe_cpu, this to prevent
+	 * deadlock when we have a kprobe on ISR routine and a kprobe on task
+	 * routine
+	 */
 	local_irq_save(flags);
+
 	spin_lock(&kprobe_lock);
 	kprobe_cpu = smp_processor_id();
+
  	local_irq_restore(flags);
 }
 
@@ -167,9 +174,16 @@ void __kprobes unlock_kprobes(void)
 {
 	unsigned long flags = 0;
 
+	/* Avoiding local interrupts to happen right after we update
+	 * kprobe_cpu and before we get a a chance to release kprobe_lock,
+	 * this to prevent deadlock when we have a kprobe on ISR routine and
+	 * a kprobe on task routine
+	 */
 	local_irq_save(flags);
+
 	kprobe_cpu = NR_CPUS;
 	spin_unlock(&kprobe_lock);
+
  	local_irq_restore(flags);
 }
 
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