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SubjectRe: [PATCH] rcu,ftrace: Fix ftrace recursion
On Tue, Sep 29, 2020 at 10:36:20AM -0400, Steven Rostedt wrote:
> On Tue, 29 Sep 2020 13:33:40 +0200
> Peter Zijlstra <peterz@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.phillips@amd.com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@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. ;-)

Thanx, Paul

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