tracing: Lock event_mutex before synth_event_mutex
synthetic event is using synth_event_mutex for protecting synth_event_list, and event_trigger_write() path acquires locks as below order. event_trigger_write(event_mutex) ->trigger_process_regex(trigger_cmd_mutex) ->event_hist_trigger_func(synth_event_mutex) On the other hand, synthetic event creation and deletion paths call trace_add_event_call() and trace_remove_event_call() which acquires event_mutex. In that case, if we keep the synth_event_mutex locked while registering/unregistering synthetic events, its dependency will be inversed. To avoid this issue, current synthetic event is using a 2 phase process to create/delete events. For example, it searches existing events under synth_event_mutex to check for event-name conflicts, and unlocks synth_event_mutex, then registers a new event under event_mutex locked. Finally, it locks synth_event_mutex and tries to add the new event to the list. But it can introduce complexity and a chance for name conflicts. To solve this simpler, this introduces trace_add_event_call_nolock() and trace_remove_event_call_nolock() which don't acquire event_mutex inside. synthetic event can lock event_mutex before synth_event_mutex to solve the lock dependency issue simpler. Link: http://lkml.kernel.org/r/154140844377.17322.13781091165954002713.stgit@devbox Reviewed-by:Tom Zanussi <tom.zanussi@linux.intel.com> Tested-by:
Tom Zanussi <tom.zanussi@linux.intel.com> Signed-off-by:
Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by:
Steven Rostedt (VMware) <rostedt@goodmis.org>
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