hw_breakpoints: Allow arch-specific cleanup before breakpoint unregistration

Certain architectures (such as PowerPC) have a need to clean up data
structures before a breakpoint is unregistered.  This introduces an
arch-specific hook in release_bp_slot() along with a weak definition
in the form of a stub function.
Signed-off-by: NK.Prasad <prasad@linux.vnet.ibm.com>
Acked-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

kernel/hw_breakpoint.c

@@ -241,6 +241,17 @@ toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
 		per_cpu(nr_cpu_bp_pinned[type], bp->cpu) -= weight;
 }
 
+/*
+ * Function to perform processor-specific cleanup during unregistration
+ */
+__weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
+{
+	/*
+	 * A weak stub function here for those archs that don't define
+	 * it inside arch/.../kernel/hw_breakpoint.c
+	 */
+}
+
 /*
  * Contraints to check before allowing this new breakpoint counter:
  *
@@ -339,6 +350,7 @@ void release_bp_slot(struct perf_event *bp)
 {
 	mutex_lock(&nr_bp_mutex);
 
+	arch_unregister_hw_breakpoint(bp);
 	__release_bp_slot(bp);
 
 	mutex_unlock(&nr_bp_mutex);