From 3ccb01239201af06a07482ec686b14cd148102a5 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Tue, 3 Dec 2013 12:41:20 -0500 Subject: tracing: Only run synchronize_sched() at instance deletion time It has been reported that boot up with FTRACE_SELFTEST enabled can take a very long time. There can be stalls of over a minute. This was tracked down to the synchronize_sched() called when a system call event is disabled. As the self tests enable and disable thousands of events, this makes the synchronize_sched() get called thousands of times. The synchornize_sched() was added with d562aff93bfb53 "tracing: Add support for SOFT_DISABLE to syscall events" which caused this regression (added in 3.13-rc1). The synchronize_sched() is to protect against the events being accessed when a tracer instance is being deleted. When an instance is being deleted all the events associated to it are unregistered. The synchronize_sched() makes sure that no more users are running when it finishes. Instead of calling synchronize_sched() for all syscall events, we only need to call it once, after the events are unregistered and before the instance is deleted. The event_mutex is held during this action to prevent new users from enabling events. Link: http://lkml.kernel.org/r/20131203124120.427b9661@gandalf.local.home Reported-by: Petr Mladek Acked-by: Tom Zanussi Acked-by: Petr Mladek Tested-by: Petr Mladek Signed-off-by: Steven Rostedt --- kernel/trace/trace_events.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'kernel/trace/trace_events.c') diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index f919a2e21bf3..a11800ae96de 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -2314,6 +2314,9 @@ int event_trace_del_tracer(struct trace_array *tr) /* Disable any running events */ __ftrace_set_clr_event_nolock(tr, NULL, NULL, NULL, 0); + /* Access to events are within rcu_read_lock_sched() */ + synchronize_sched(); + down_write(&trace_event_sem); __trace_remove_event_dirs(tr); debugfs_remove_recursive(tr->event_dir); -- cgit v1.2.2