On Fri, 20 Nov 2020 19:17:37 +0100
Marco Elver [off-list ref] wrote:

quoted

quoted

quoted

+++ b/kernel/rcu/Makefile

@@ -3,6 +3,13 @@
 # and is generally not a function of system call inputs.
 KCOV_INSTRUMENT := n

+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_update.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_sync.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_srcutree.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_tree.o = $(CC_FLAGS_FTRACE)
+endif
+

Can you narrow it down further? That is, do you really need all of the
above to stop the stalls?

I tried to reduce it to 1 or combinations of 2 files only, but that
didn't work.

I'm curious if this would help at all?

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2a52f42f64b6..d020ecefd151 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c

@@ -1094,7 +1094,7 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
  * if the current CPU is not in its idle loop or is in an interrupt or
  * NMI handler, return true.
  */
-bool rcu_is_watching(void)
+notrace bool rcu_is_watching(void)
 {
        bool ret;

Although I don't see it in the recursion list.