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[5.10,168/717] rcu,ftrace: Fix ftrace recursion

Message ID 20201228125029.005848859@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman Dec. 28, 2020, 12:42 p.m. UTC 
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 mbox series

Patch

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;