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    SubjectRe: [PATCH v10 2/3] tracepoint: Make rcuidle tracepoint callers use SRCU
    On Tue, Jul 17, 2018 at 08:25:28PM +0200, Peter Zijlstra wrote:
    > On Fri, Jul 13, 2018 at 02:55:46PM -0700, Joel Fernandes wrote:
    > > + /* keep srcu and sched-rcu usage consistent */ \
    > > + preempt_disable_notrace(); \
    > > + \
    > > + /* \
    > > + * For rcuidle callers, use srcu since sched-rcu \
    > > + * doesn't work from the idle path. \
    > > + */ \
    > > + if (rcuidle) \
    > > + idx = srcu_read_lock_notrace(&tracepoint_srcu); \
    > > + else \
    > > + rcu_read_lock_sched_notrace(); \
    >
    > That else is completely superfluous. rcu_read_lock_sched_notrace() :=
    > prempt_disable_notrace().

    I have a patch as below on top of this series. Thanks for the suggestion.

    Steve, Peter,

    Is it Ok with you to take the below patch ontop of this series? I avoided
    resending the 3-patch series since this is the only change, but let me know
    what you prefer or makes it easy for you.

    ------->8--------

    From: Joel Fernandes <joelaf@google.com>
    Subject: [PATCH] tracepoint: Remove extra unneeded rcu_read_lock_sched_notrace

    A great idea was provided that rcu_read_lock_sched_notrace being the
    equivalent of preempt_disable_notrace is unnecessary to call in
    tracepoint code, since we already call preempt_disable_notrace in
    advance. So lets remove the extra call.

    Suggested-by: Peter Zijlstra <peterz@infradead.org>
    Signed-off-by: Joel Fernandes <joelaf@google.com>
    ---
    include/linux/tracepoint.h | 4 ----
    1 file changed, 4 deletions(-)

    diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
    index 97e1d365a817..6e7bc6ebfcd8 100644
    --- a/include/linux/tracepoint.h
    +++ b/include/linux/tracepoint.h
    @@ -161,8 +161,6 @@ extern void syscall_unregfunc(void);
    */ \
    if (rcuidle) \
    idx = srcu_read_lock_notrace(&tracepoint_srcu); \
    - else \
    - rcu_read_lock_sched_notrace(); \
    \
    it_func_ptr = rcu_dereference_raw((tp)->funcs); \
    \
    @@ -176,8 +174,6 @@ extern void syscall_unregfunc(void);
    \
    if (rcuidle) \
    srcu_read_unlock_notrace(&tracepoint_srcu, idx);\
    - else \
    - rcu_read_unlock_sched_notrace(); \
    \
    preempt_enable_notrace(); \
    } while (0)
    --
    2.18.0.203.gfac676dfb9-goog
    \
     
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