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Subject[019/116] tracing: Use same local variable when resetting the ring buffer
2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Steven Rostedt <srostedt@redhat.com>

commit 283740c619d211e34572cc93c8cdba92ccbdb9cc upstream.

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.

Reported-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
kernel/trace/trace.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -748,10 +748,10 @@ out:
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();
}

@@ -763,7 +763,7 @@ void tracing_reset(struct trace_array *t

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

ring_buffer_record_enable(buffer);
}
@@ -781,7 +781,7 @@ void tracing_reset_online_cpus(struct 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);
}



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