From: Steven Rostedt <srostedt@redhat.com>
Date: Sat, 13 Mar 2010 00:48:41 +0000 (-0500)
Subject: tracing: Use same local variable when resetting the ring buffer
X-Git-Tag: v2.6.34-rc2~52^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=283740c619d211e34572cc93c8cdba92ccbdb9cc;p=pandora-kernel.git

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>
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