From 5f71e693df3a02dc436ed383276e85bdcb8cb4bf Mon Sep 17 00:00:00 2001
From: Neil Leeder <nleeder@codeaurora.org>
Date: Thu, 24 Sep 2015 12:14:20 -0400
Subject: perf: stop deadlock if attempt to bring cpu up fails

When an attempt is made to free an event on a CPU which is
no longer online, perf tries to bring the CPU online. This
can fail, resulting in an UP_CANCELLED notifier, which
eventually tries to acquire the ctx->mutex which is already
being held by the code, which brings up the CPU.

Removing the attempt to bring the cpu up will remove this
deadlock, but also requires temporarily removing support of
counting events across hotplug. This will be restored in a
later patch.

Conflicts:
	kernel/events/core.c
	kernel/events/hw_breakpoint.c

Change-Id: Iaafa3c6688d26508857472fd5bb32139a137880e
Signed-off-by: Neil Leeder <nleeder@codeaurora.org>
---
 kernel/events/core.c          | 39 +--------------------------------------
 kernel/events/hw_breakpoint.c |  2 --
 2 files changed, 1 insertion(+), 40 deletions(-)

(limited to 'kernel')

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6cd152e99891..7fee87daac56 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1693,33 +1693,7 @@ static int __perf_remove_from_context(void *info)
 	return 0;
 }
 
-
-#ifdef CONFIG_SMP
-static void perf_retry_remove(struct perf_event *event,
-			      struct remove_event *rep)
-{
-	int up_ret;
-	/*
-	 * CPU was offline. Bring it online so we can
-	 * gracefully exit a perf context.
-	 */
-	up_ret = cpu_up(event->cpu);
-	if (!up_ret)
-		/* Try the remove call once again. */
-		cpu_function_call(event->cpu, __perf_remove_from_context,
-				  rep);
-	else
-		pr_err("Failed to bring up CPU: %d, ret: %d\n",
-		       event->cpu, up_ret);
-}
-#else
-static void perf_retry_remove(struct perf_event *event,
-			      struct remove_event *rep)
-{
-}
-#endif
-
- /*
+/*
  * Remove the event from a task's (or a CPU's) list of events.
  *
  * CPU events are removed with a smp call. For task events we only
@@ -1754,9 +1728,6 @@ static void __ref perf_remove_from_context(struct perf_event *event,
 		 */
 		ret = cpu_function_call(event->cpu, __perf_remove_from_context,
 					&re);
-		if (ret == -ENXIO)
-			perf_retry_remove(event, &re);
-
 		return;
 	}
 
@@ -7138,8 +7109,6 @@ static struct pmu perf_swevent = {
 	.start		= perf_swevent_start,
 	.stop		= perf_swevent_stop,
 	.read		= perf_swevent_read,
-
-	.events_across_hotplug = 1,
 };
 
 #ifdef CONFIG_EVENT_TRACING
@@ -7261,8 +7230,6 @@ static struct pmu perf_tracepoint = {
 	.start		= perf_swevent_start,
 	.stop		= perf_swevent_stop,
 	.read		= perf_swevent_read,
-
-	.events_across_hotplug = 1,
 };
 
 static inline void perf_tp_register(void)
@@ -7550,8 +7517,6 @@ static struct pmu perf_cpu_clock = {
 	.start		= cpu_clock_event_start,
 	.stop		= cpu_clock_event_stop,
 	.read		= cpu_clock_event_read,
-
-	.events_across_hotplug = 1,
 };
 
 /*
@@ -7633,8 +7598,6 @@ static struct pmu perf_task_clock = {
 	.start		= task_clock_event_start,
 	.stop		= task_clock_event_stop,
 	.read		= task_clock_event_read,
-
-	.events_across_hotplug = 1,
 };
 
 static void perf_pmu_nop_void(struct pmu *pmu)
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 7da5b674d16e..92ce5f4ccc26 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -614,8 +614,6 @@ static struct pmu perf_breakpoint = {
 	.start		= hw_breakpoint_start,
 	.stop		= hw_breakpoint_stop,
 	.read		= hw_breakpoint_pmu_read,
-
-	.events_across_hotplug = 1,
 };
 
 int __init init_hw_breakpoint(void)
-- 
cgit v1.2.3