Commit 283740c6 authored Mar 12, 2010 by Steven Rostedt Committed by Steven Rostedt Mar 12, 2010

tracing: Use same local variable when resetting the ring buffer



In the ftrace code that resets the ring buffer it references the
buffer with a local variable, but then uses the tr->buffer as the
parameter to reset. If the wakeup tracer is running, which can
switch the tr->buffer with the max saved buffer, this can break
the requirement of disabling the buffer before the reset.

   buffer = tr->buffer;
   ring_buffer_record_disable(buffer);
   synchronize_sched();
   __tracing_reset(tr->buffer, cpu);

If the tr->buffer is swapped, then the reset is not happening to the
buffer that was disabled. This will cause the ring buffer to fail.

Found with Li Zefan's ftrace_stress_test.

Cc: stable@kernel.org
Reported-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent ea14eb71

kernel/trace/trace.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -840,10 +840,10 @@ void unregister_tracer(struct tracer *type)
		mutex_unlock(&trace_types_lock);
		}

		static void __tracing_reset(struct trace_array *tr, int cpu)
		static void __tracing_reset(struct ring_buffer *buffer, int cpu)
		{
		ftrace_disable_cpu();
		ring_buffer_reset_cpu(tr->buffer, cpu);
		ring_buffer_reset_cpu(buffer, cpu);
		ftrace_enable_cpu();
		}

		@@ -855,7 +855,7 @@ void tracing_reset(struct trace_array *tr, int cpu)

		/* Make sure all commits have finished */
		synchronize_sched();
		__tracing_reset(tr, cpu);
		__tracing_reset(buffer, cpu);

		ring_buffer_record_enable(buffer);
		}
		@@ -873,7 +873,7 @@ void tracing_reset_online_cpus(struct trace_array *tr)
		tr->time_start = ftrace_now(tr->cpu);

		for_each_online_cpu(cpu)
		__tracing_reset(tr, cpu);
		__tracing_reset(buffer, cpu);

		ring_buffer_record_enable(buffer);
		}