Commit 09d8091c authored Jul 23, 2013 by Steven Rostedt (Red Hat) Committed by Steven Rostedt Jul 26, 2013

tracing: Remove locking trace_types_lock from tracing_reset_all_online_cpus()

Commit a8227415 "tracing: Protect ftrace_trace_arrays list in trace_events.c"
added taking the trace_types_lock mutex in trace_events.c as there were
several locations that needed it for protection. Unfortunately, it also
encapsulated a call to tracing_reset_all_online_cpus() which also takes
the trace_types_lock, causing a deadlock.

This happens when a module has tracepoints and has been traced. When the
module is removed, the trace events module notifier will grab the
trace_types_lock, do a bunch of clean ups, and also clears the buffer
by calling tracing_reset_all_online_cpus. This doesn't happen often
which explains why it wasn't caught right away.

Commit a8227415 was marked for stable, which means this must be
sent to stable too.

Link: http://lkml.kernel.org/r/51EEC646.7070306@broadcom.com



Reported-by: Arend van Spril <arend@broadcom.com>
Tested-by: Arend van Spriel <arend@broadcom.com>
Cc: Alexander Z Lam <azl@google.com>
Cc: Vaibhav Nagarnaik <vnagarnaik@google.com>
Cc: David Sharp <dhsharp@google.com>
Cc: stable@vger.kernel.org # 3.10
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent 195a8afc

kernel/trace/trace.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -1224,18 +1224,17 @@ void tracing_reset_current(int cpu)
		tracing_reset(&global_trace.trace_buffer, cpu);
		}

		/* Must have trace_types_lock held */
		void tracing_reset_all_online_cpus(void)
		{
		struct trace_array *tr;

		mutex_lock(&trace_types_lock);
		list_for_each_entry(tr, &ftrace_trace_arrays, list) {
		tracing_reset_online_cpus(&tr->trace_buffer);
		#ifdef CONFIG_TRACER_MAX_TRACE
		tracing_reset_online_cpus(&tr->max_buffer);
		#endif
		}
		mutex_unlock(&trace_types_lock);
		}

		#define SAVED_CMDLINES 128