On Tue, Sep 29, 2020 at 10:54:16AM -0400, Steven Rostedt wrote: > On Tue, 29 Sep 2020 07:41:06 -0700 > "Paul E. McKenney" <paul...@kernel.org> wrote: > > > On Tue, Sep 29, 2020 at 10:36:20AM -0400, Steven Rostedt wrote: > > > On Tue, 29 Sep 2020 13:33:40 +0200 > > > Peter Zijlstra <pet...@infradead.org> wrote: > > > > > > > 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. Probably due to there not being a helpful > > > > comment. > > > > > > > > Reinstate the notrace and add a comment to avoid loosing it again. > > > > > > > > Fixes: ff5c4f5cad33 ("rcu/tree: Mark the idle relevant functions > > > > noinstr") > > > > Reported-by: Kim Phillips <kim.phill...@amd.com> > > > > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.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 ee5e595501e8..33020d84ec6b 100644 > > > > --- a/kernel/rcu/tree.c > > > > +++ b/kernel/rcu/tree.c > > > > @@ -1098,8 +1098,11 @@ noinstr bool __rcu_is_watching(void) > > > > * 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. > > > > + * > > > > + * Must be notrace because __ftrace_ops_list_func() / > > > > ftrace_ops_assist_func() > > > > + * will call this (for every function) outside of recursion protection. > > > > */ > > > > -bool rcu_is_watching(void) > > > > +notrace bool rcu_is_watching(void) > > > > { > > > > bool ret; > > > > > > > > > > I think the patch I suggested is more suitable. > > > > OK, I will let you guys fight it out. ;-) > > > > Well, I think we should actually apply both, but the comment needs to be > updated, as it will no longer be outside recursion. And the comment is > wrong now as well, as its only outside recursion protection for the > assist_func(). > > But it does prevent it from being always called for perf. > > * Make notrace because it can be called by the internal functions of > * ftrace, and making this notrace removes unnecessary recursion calls.
Fair enough. ;-) If I don't hear otherwise by late today (Tuesday), Pacific Time, I will update the comment and pull it into -rcu. If you guys have some other route to mainline in mind, you have my Reviewed-by. Either way, just let me know. Thanx, Paul