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rcu,ftrace: Fix ftrace recursion 

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

  ff5c4f5cad ("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: ff5c4f5cad ("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>
This commit is contained in:
Peter Zijlstra 2020-09-29 13:33:40 +02:00 committed by Paul E. McKenney
parent 7c47ee5aa0
commit d2098b4440
1 changed files with 4 additions and 1 deletions
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5
kernel/rcu/tree.c
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@ -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;