lkml.org 
[lkml]   [2019]   [Jul]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH v1 1/6] rcu: Add support for consolidated-RCU reader checking
On Fri, Jul 12, 2019 at 01:11:25PM +0200, Peter Zijlstra wrote:
> On Thu, Jul 11, 2019 at 07:43:56PM -0400, Joel Fernandes (Google) wrote:
> > +int rcu_read_lock_any_held(void)
> > +{
> > + int lockdep_opinion = 0;
> > +
> > + if (!debug_lockdep_rcu_enabled())
> > + return 1;
> > + if (!rcu_is_watching())
> > + return 0;
> > + if (!rcu_lockdep_current_cpu_online())
> > + return 0;
> > +
> > + /* Preemptible RCU flavor */
> > + if (lock_is_held(&rcu_lock_map))
>
> you forgot debug_locks here.

Actually, it turns out debug_locks checking is not even needed. If
debug_locks == 0, then debug_lockdep_rcu_enabled() returns 0 and we would not
get to this point.

> > + return 1;
> > +
> > + /* BH flavor */
> > + if (in_softirq() || irqs_disabled())
>
> I'm not sure I'd put irqs_disabled() under BH, also this entire
> condition is superfluous, see below.
>
> > + return 1;
> > +
> > + /* Sched flavor */
> > + if (debug_locks)
> > + lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> > + return lockdep_opinion || !preemptible();
>
> that !preemptible() turns into:
>
> !(preempt_count()==0 && !irqs_disabled())
>
> which is:
>
> preempt_count() != 0 || irqs_disabled()
>
> and already includes irqs_disabled() and in_softirq().
>
> > +}
>
> So maybe something lke:
>
> if (debug_locks && (lock_is_held(&rcu_lock_map) ||
> lock_is_held(&rcu_sched_lock_map)))
> return true;

Agreed, I will do it this way (without the debug_locks) like:

---8<-----------------------

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index ba861d1716d3..339aebc330db 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -296,27 +296,15 @@ EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);

int rcu_read_lock_any_held(void)
{
- int lockdep_opinion = 0;
-
if (!debug_lockdep_rcu_enabled())
return 1;
if (!rcu_is_watching())
return 0;
if (!rcu_lockdep_current_cpu_online())
return 0;
-
- /* Preemptible RCU flavor */
- if (lock_is_held(&rcu_lock_map))
- return 1;
-
- /* BH flavor */
- if (in_softirq() || irqs_disabled())
- return 1;
-
- /* Sched flavor */
- if (debug_locks)
- lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
- return lockdep_opinion || !preemptible();
+ if (lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map))
+ return 1;
+ return !preemptible();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);

\
 
 \ /
  Last update: 2019-07-12 17:12    [W:0.076 / U:36.624 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site