On Tue, Jul 16, 2019 at 11:53:03AM -0700, Paul E. McKenney wrote:
[snip]

quoted

quoted

A few more things below.

quoted

---
 include/linux/rculist.h  | 28 ++++++++++++++++++++-----
 include/linux/rcupdate.h |  7 +++++++
 kernel/rcu/Kconfig.debug | 11 ++++++++++
 kernel/rcu/update.c      | 44 ++++++++++++++++++++++++----------------
 4 files changed, 67 insertions(+), 23 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index e91ec9ddcd30..1048160625bb 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h

@@ -40,6 +40,20 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
  */
 #define list_next_rcu(list)	(*((struct list_head __rcu **)(&(list)->next)))
 
+/*
+ * Check during list traversal that we are within an RCU reader
+ */
+
+#ifdef CONFIG_PROVE_RCU_LIST

This new Kconfig option is OK temporarily, but unless there is reason to
fear malfunction that a few weeks of rcutorture, 0day, and -next won't
find, it would be better to just use CONFIG_PROVE_RCU.  The overall goal
is to reduce the number of RCU knobs rather than grow them, must though
history might lead one to believe otherwise.  :-/

If you want, we can try to drop this option and just use PROVE_RCU however I
must say there may be several warnings that need to be fixed in a short
period of time (even a few weeks may be too short) considering the 1000+
uses of RCU lists.

Do many people other than me build with CONFIG_PROVE_RCU?  If so, then
that would be a good reason for a temporary CONFIG_PROVE_RCU_LIST,
as in going away in a release or two once the warnings get fixed.

PROVE_RCU is enabled by default with PROVE_LOCKING, so it is used quite
heavilty.

quoted

But I don't mind dropping it and it may just accelerate the fixing up of all
callers.

I will let you decide based on the above question.  But if you have
CONFIG_PROVE_RCU_LIST, as noted below, it needs to depend on RCU_EXPERT.

Ok, will make it depend. But yes for temporary purpose, I will leave it as a
config and remove it later.

thanks,

 - Joel