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A regression showed up that there's a large delay when enabling

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all events. This was prevalent when FTRACE_SELFTEST was enabled which
 enables all events several times, and caused the system bootup to
 pause for over a minute.
 
 This was tracked down to an addition of a synchronize_sched() performed
 when system call tracepoints are unregistered.
 
 The synchronize_sched() is needed between the unregistering of the
 system call tracepoint and a deletion of a tracing instance buffer.
 But placing the synchronize_sched() in the unreg of *every* system call
 tracepoint is a bit overboard. A single synchronize_sched() before
 the deletion of the instance is sufficient.
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Merge tag 'trace-fixes-3.13-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fix from Steven Rostedt:
 "A regression showed up that there's a large delay when enabling all
  events.  This was prevalent when FTRACE_SELFTEST was enabled which
  enables all events several times, and caused the system bootup to
  pause for over a minute.

  This was tracked down to an addition of a synchronize_sched()
  performed when system call tracepoints are unregistered.

  The synchronize_sched() is needed between the unregistering of the
  system call tracepoint and a deletion of a tracing instance buffer.
  But placing the synchronize_sched() in the unreg of *every* system
  call tracepoint is a bit overboard.  A single synchronize_sched()
  before the deletion of the instance is sufficient"

* tag 'trace-fixes-3.13-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Only run synchronize_sched() at instance deletion time
This commit is contained in:
Linus Torvalds 2013-12-06 08:34:16 -08:00
commit 843f4f4bb1
2 changed files with 3 additions and 10 deletions
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3
kernel/trace/trace_events.c
View file

@ -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);

10
kernel/trace/trace_syscalls.c
View file

@ -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)