perf/hwpb: Invoke __perf_event_disable() if interrupts are already disabled

While debugging a warning message on PowerPC while using hardware
breakpoints, it was discovered that when perf_event_disable is invoked
through hw_breakpoint_handler function with interrupts disabled, a
subsequent IPI in the code path would trigger a WARN_ON_ONCE message in
smp_call_function_single function.

This patch calls __perf_event_disable() when interrupts are already
disabled, instead of perf_event_disable().

Reported-by: Edjunior Barbosa Machado <emachado@linux.vnet.ibm.com>
Signed-off-by: K.Prasad <Prasad.Krishnan@gmail.com>
[naveen.n.rao@linux.vnet.ibm.com: v3: Check to make sure we target current task]
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120802081635.5811.17737.stgit@localhost.localdomain
[ Fixed build error on MIPS. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/perf_event.h

@@ -1296,6 +1296,7 @@ extern int perf_swevent_get_recursion_context(void);
 extern void perf_swevent_put_recursion_context(int rctx);
 extern void perf_event_enable(struct perf_event *event);
 extern void perf_event_disable(struct perf_event *event);
+extern int __perf_event_disable(void *info);
 extern void perf_event_task_tick(void);
 #else
 static inline void
@@ -1334,6 +1335,7 @@ static inline int  perf_swevent_get_recursion_context(void)		{ return -1; }
 static inline void perf_swevent_put_recursion_context(int rctx)		{ }
 static inline void perf_event_enable(struct perf_event *event)		{ }
 static inline void perf_event_disable(struct perf_event *event)		{ }
+static inline int __perf_event_disable(void *info)			{ return -1; }
 static inline void perf_event_task_tick(void)				{ }
 #endif
 

kernel/events/core.c

@@ -1253,7 +1253,7 @@ retry:
 /*
  * Cross CPU call to disable a performance event
  */
-static int __perf_event_disable(void *info)
+int __perf_event_disable(void *info)
 {
 	struct perf_event *event = info;
 	struct perf_event_context *ctx = event->ctx;

kernel/events/hw_breakpoint.c

@@ -453,7 +453,16 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
 	int old_type = bp->attr.bp_type;
 	int err = 0;
 
-	perf_event_disable(bp);
+	/*
+	 * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
+	 * will not be possible to raise IPIs that invoke __perf_event_disable.
+	 * So call the function directly after making sure we are targeting the
+	 * current task.
+	 */
+	if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
+		__perf_event_disable(bp);
+	else
+		perf_event_disable(bp);
 
 	bp->attr.bp_addr = attr->bp_addr;
 	bp->attr.bp_type = attr->bp_type;