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    Subject[PATCH v2 7/9] tracing: Employ trace_rcu_{enter,exit}()
    Replace the opencoded (and incomplete) RCU manipulations with the new
    helpers to ensure a regular RCU context when calling into
    __ftrace_trace_stack().

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    ---
    kernel/trace/trace.c | 19 +++----------------
    1 file changed, 3 insertions(+), 16 deletions(-)

    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -2989,24 +2989,11 @@ void __trace_stack(struct trace_array *t
    int pc)
    {
    struct trace_buffer *buffer = tr->array_buffer.buffer;
    + unsigned long rcu_flags;

    - if (rcu_is_watching()) {
    - __ftrace_trace_stack(buffer, flags, skip, pc, NULL);
    - return;
    - }
    -
    - /*
    - * When an NMI triggers, RCU is enabled via rcu_nmi_enter(),
    - * but if the above rcu_is_watching() failed, then the NMI
    - * triggered someplace critical, and rcu_irq_enter() should
    - * not be called from NMI.
    - */
    - if (unlikely(in_nmi()))
    - return;
    -
    - rcu_irq_enter_irqsave();
    + rcu_flags = trace_rcu_enter();
    __ftrace_trace_stack(buffer, flags, skip, pc, NULL);
    - rcu_irq_exit_irqsave();
    + trace_rcu_exit(rcu_flags);
    }

    /**

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