Re: [BUG] ftrace: WARNING: suspicious RCU usage

From: Paul E. McKenney
Date: Tue Jun 27 2017 - 20:45:04 EST


On Tue, Jun 27, 2017 at 06:57:43PM -0400, Steven Rostedt wrote:
> On Wed, 28 Jun 2017 07:52:22 +0900
> Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index e354e47..442b409 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -973,8 +973,10 @@ static void rcu_eqs_exit(bool user)
> > if (oldval & DYNTICK_TASK_NEST_MASK) {
> > rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
> > } else {
> > + __this_cpu_inc(disable_rcu_irq_enter);
> > rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
> > rcu_eqs_exit_common(oldval, user);
> > + __this_cpu_dec(disable_rcu_irq_enter);
> > }
> > }
> >
>
> Looks like a good fix to me. Paul want to take this one?
>
> Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

Why not?

How urgent is this, as in what release do you need it in? (Default at
this point being v4.14, but non-default available upon request.)

Thanx, Paul

------------------------------------------------------------------------

commit 2165b0a9bb37f0560f261986783e7c02bb37c353
Author: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Date: Tue Jun 27 17:41:25 2017 -0700

rcu/tracing: Set disable_rcu_irq_enter on rcu_eqs_exit()

Set disable_rcu_irq_enter on not only rcu_eqs_enter_common() but also
rcu_eqs_exit(), since rcu_eqs_exit() suffers from the same issue as was
fixed for rcu_eqs_enter_common() by commit 03ecd3f48e57 ("rcu/tracing:
Add rcu_disabled to denote when rcu_irq_enter() will not work").

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ca3076b073e4..2a6b610ef54f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -952,8 +952,10 @@ static void rcu_eqs_exit(bool user)
if (oldval & DYNTICK_TASK_NEST_MASK) {
rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
} else {
+ __this_cpu_inc(disable_rcu_irq_enter);
rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
rcu_eqs_exit_common(oldval, user);
+ __this_cpu_dec(disable_rcu_irq_enter);
}
}