Messages in this thread | | | Date | Tue, 16 Jun 2015 11:37:38 -0400 | From | Steven Rostedt <> | Subject | Re: call_rcu from trace_preempt |
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On Tue, 16 Jun 2015 05:27:33 -0700 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> On Mon, Jun 15, 2015 at 10:45:05PM -0700, Alexei Starovoitov wrote: > > On 6/15/15 7:14 PM, Paul E. McKenney wrote: > > > > > >Why do you believe that it is better to fix it within call_rcu()? > > > > found it: > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index 8cf7304b2867..a3be09d482ae 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -935,9 +935,9 @@ bool notrace rcu_is_watching(void) > > { > > bool ret; > > > > - preempt_disable(); > > + preempt_disable_notrace(); > > ret = __rcu_is_watching(); > > - preempt_enable(); > > + preempt_enable_notrace(); > > return ret; > > } > > > > the rcu_is_watching() and __rcu_is_watching() are already marked > > notrace, so imo it's a good 'fix'. > > What was happening is that the above preempt_enable was triggering > > recursive call_rcu that was indeed messing 'rdp' that was > > prepared by __call_rcu and before __call_rcu_core could use that. > > > btw, also noticed that local_irq_save done by note_gp_changes > > is partially redundant. In __call_rcu_core path the irqs are > > already disabled. >
If rcu_is_watching() and __rcu_is_watching() are both marked as notrace, it makes sense to use preempt_disable/enable_notrace() as it otherwise defeats the purpose of the notrace markers on rcu_is_watching.
That is regardless of what the rest of this thread is about.
-- Steve
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