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    Subject[PATCH 5.10 168/717] rcu,ftrace: Fix ftrace recursion
    Date
    From: Peter Zijlstra <peterz@infradead.org>

    [ Upstream commit d2098b4440981705e844c50254540ba7b5f82795 ]

    Kim reported that perf-ftrace made his box unhappy. It turns out that
    commit:

    ff5c4f5cad33 ("rcu/tree: Mark the idle relevant functions noinstr")

    removed one too many notrace qualifiers, probably due to there not being
    a helpful comment.

    This commit therefore reinstates the notrace and adds a comment to avoid
    losing it again.

    [ paulmck: Apply Steven Rostedt's feedback on the comment. ]
    Fixes: ff5c4f5cad33 ("rcu/tree: Mark the idle relevant functions noinstr")
    Reported-by: Kim Phillips <kim.phillips@amd.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/rcu/tree.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
    index 655ade095e043..585bf112ee08d 100644
    --- a/kernel/rcu/tree.c
    +++ b/kernel/rcu/tree.c
    @@ -1093,8 +1093,11 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
    * CPU can safely enter RCU read-side critical sections. In other words,
    * if the current CPU is not in its idle loop or is in an interrupt or
    * NMI handler, return true.
    + *
    + * Make notrace because it can be called by the internal functions of
    + * ftrace, and making this notrace removes unnecessary recursion calls.
    */
    -bool rcu_is_watching(void)
    +notrace bool rcu_is_watching(void)
    {
    bool ret;

    --
    2.27.0


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