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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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