lkml.org 
[lkml]   [2017]   [Aug]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] perf: Explain perf_sched_mutex
Date
To clarify why atomic_inc_return(&perf_sched_events) is not sufficient and
a mutex is needed to order static branch enabling vs the atomic counter
increment, this adds a comment with an short explanation.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
kernel/events/core.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index efe09b8c38..2c8719b635 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9569,6 +9569,11 @@ static void account_event(struct perf_event *event)
inc = true;

if (inc) {
+ /*
+ * We need the mutex here because static_branch_enable()
+ * must complete *before* the perf_sched_count increment
+ * becomes visible.
+ */
if (atomic_inc_not_zero(&perf_sched_count))
goto enabled;

--
2.14.1
\
 
 \ /
  Last update: 2017-08-29 16:02    [W:0.053 / U:0.168 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site