[PATCH 3.2 025/153] perf/hwpb: Invoke __perf_event_disable() if interrupts are already disabled

[Ben Hutchings]

3.2.102-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "K.Prasad" <Prasad.Krishnan@xxxxxxxxx>

commit 500ad2d8b01390c98bc6dce068bccfa9534b8212 upstream.

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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: K.Prasad <Prasad.Krishnan@xxxxxxxxx>
[naveen.n.rao@xxxxxxxxxxxxxxxxxx: v3: Check to make sure we target current task]
Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Acked-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20120802081635.5811.17737.stgit@xxxxxxxxxxxxxxxxxxxxx
[ Fixed build error on MIPS. ]
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 include/linux/perf_event.h    |  2 ++
 kernel/events/core.c          |  2 +-
 kernel/events/hw_breakpoint.c | 11 ++++++++++-
 3 files changed, 13 insertions(+), 2 deletions(-)

--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1140,6 +1140,7 @@ extern int perf_swevent_get_recursion_co
 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
@@ -1178,6 +1179,7 @@ static inline int  perf_swevent_get_recu
 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
 
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1344,7 +1344,7 @@ 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;
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -453,7 +453,16 @@ int modify_user_hw_breakpoint(struct per
 	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;