Commit a2f80714 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
Browse files

tracing: Disable buffer switching when starting or stopping trace



When the trace iterator is read, tracing_start() and tracing_stop()
is called to stop tracing while the iterator is processing the trace
output.

These functions disable both the standard buffer and the max latency
buffer. But if the wakeup tracer is running, it can switch these
buffers between the two disables:

  buffer = global_trace.buffer;
  if (buffer)
      ring_buffer_record_disable(buffer);

      <<<--------- swap happens here

  buffer = max_tr.buffer;
  if (buffer)
      ring_buffer_record_disable(buffer);

What happens is that we disabled the same buffer twice. On tracing_start()
we can enable the same buffer twice. All ring_buffer_record_disable()
must be matched with a ring_buffer_record_enable() or the buffer
can be disable permanently, or enable prematurely, and cause a bug
where a reset happens while a trace is commiting.

This patch protects these two by taking the ftrace_max_lock to prevent
a switch from occurring.

Found with Li Zefan's ftrace_stress_test.

Cc: stable@kernel.org
Reported-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 283740c6
......@@ -950,6 +950,8 @@ void tracing_start(void)
goto out;
}
/* Prevent the buffers from switching */
arch_spin_lock(&ftrace_max_lock);
buffer = global_trace.buffer;
if (buffer)
......@@ -959,6 +961,8 @@ void tracing_start(void)
if (buffer)
ring_buffer_record_enable(buffer);
arch_spin_unlock(&ftrace_max_lock);
ftrace_start();
out:
spin_unlock_irqrestore(&tracing_start_lock, flags);
......@@ -980,6 +984,9 @@ void tracing_stop(void)
if (trace_stop_count++)
goto out;
/* Prevent the buffers from switching */
arch_spin_lock(&ftrace_max_lock);
buffer = global_trace.buffer;
if (buffer)
ring_buffer_record_disable(buffer);
......@@ -988,6 +995,8 @@ void tracing_stop(void)
if (buffer)
ring_buffer_record_disable(buffer);
arch_spin_unlock(&ftrace_max_lock);
out:
spin_unlock_irqrestore(&tracing_start_lock, flags);
}
......
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