[PATCH v2] Hardware breakpoints: Invoke __perf_event_disable() if interrupts are already disabled

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

From: K.Prasad <Prasad.Krishnan@gmail.com>

My apologies. I missed the From header in my previous mail.

---
Please find v2 of the patch from Prasad, based on Peter Zijlstra's
feedback. This applies on top of v3.5-rc5. This has been tested and
found to work fine by Edjunior.

Regards,
Naveen

---
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>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 include/linux/perf_event.h    |    2 ++
 kernel/events/core.c          |    2 +-
 kernel/events/hw_breakpoint.c |   10 +++++++++-
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 45db49f..c289ba0 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1292,6 +1292,7 @@ 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
@@ -1330,6 +1331,7 @@ 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)			{ }
 static inline void perf_event_task_tick(void)				{ }
 #endif
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index d7d71d6..0ad0fc9 100644
--- a/kernel/events/core.c
+++ b/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;
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index bb38c4d..483f14a 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -453,7 +453,15 @@ 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.
+	 */
+	if (irqs_disabled())
+		__perf_event_disable(bp);
+	else
+		perf_event_disable(bp);
 
 	bp->attr.bp_addr = attr->bp_addr;
 	bp->attr.bp_type = attr->bp_type;