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| author | Steven Rostedt <rostedt@goodmis.org> | 2013-12-03 12:41:20 -0500 |
|---|---|---|
| committer | Steven Rostedt <rostedt@goodmis.org> | 2013-12-05 14:22:30 -0500 |
| commit | 3ccb01239201af06a07482ec686b14cd148102a5 (patch) | |
| tree | 5ad078061e71dcf23cd1ee3f4ca353060c185324 | |
| parent | dc1ccc48159d63eca5089e507c82c7d22ef60839 (diff) | |
| download | lwn-3ccb01239201af06a07482ec686b14cd148102a5.tar.gz lwn-3ccb01239201af06a07482ec686b14cd148102a5.zip | |
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 <pmladek@suse.cz>
Acked-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Acked-by: Petr Mladek <pmladek@suse.cz>
Tested-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
| -rw-r--r-- | kernel/trace/trace_events.c | 3 | ||||
| -rw-r--r-- | kernel/trace/trace_syscalls.c | 10 |
2 files changed, 3 insertions, 10 deletions
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); diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c index e4b6d11bdf78..ea90eb5f6f17 100644 --- a/kernel/trace/trace_syscalls.c +++ b/kernel/trace/trace_syscalls.c @@ -431,11 +431,6 @@ static void unreg_event_syscall_enter(struct ftrace_event_file *file, if (!tr->sys_refcount_enter) unregister_trace_sys_enter(ftrace_syscall_enter, tr); mutex_unlock(&syscall_trace_lock); - /* - * Callers expect the event to be completely disabled on - * return, so wait for current handlers to finish. - */ - synchronize_sched(); } static int reg_event_syscall_exit(struct ftrace_event_file *file, @@ -474,11 +469,6 @@ static void unreg_event_syscall_exit(struct ftrace_event_file *file, if (!tr->sys_refcount_exit) unregister_trace_sys_exit(ftrace_syscall_exit, tr); mutex_unlock(&syscall_trace_lock); - /* - * Callers expect the event to be completely disabled on - * return, so wait for current handlers to finish. - */ - synchronize_sched(); } static int __init init_syscall_trace(struct ftrace_event_call *call) |