Messages in this thread | | | Date | Fri, 6 Sep 2013 08:18:52 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical section? |
| |
On Fri, Sep 06, 2013 at 12:59:41PM +0200, Frederic Weisbecker wrote: > On Thu, Sep 05, 2013 at 12:52:34PM -0700, Paul E. McKenney wrote: > > There is currently no way for kernel code to determine whether it > > is safe to enter an RCU read-side critical section, in other words, > > whether or not RCU is paying attention to the currently running CPU. > > Given the large and increasing quantity of code shared by the idle loop > > and non-idle code, the this shortcoming is becoming increasingly painful. > > > > This commit therefore adds rcu_watching_this_cpu(), which returns true > > if it is safe to enter an RCU read-side critical section on the currently > > running CPU. This function is quite fast, using only a __this_cpu_read(). > > However, the caller must disable preemption. > > > > Reported-by: Steven Rostedt <rostedt@goodmis.org> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > > > include/linux/rcupdate.h | 1 + > > kernel/rcutree.c | 12 ++++++++++++ > > 2 files changed, 13 insertions(+) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 15d33d9..1c7112c 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -225,6 +225,7 @@ extern void rcu_idle_enter(void); > > extern void rcu_idle_exit(void); > > extern void rcu_irq_enter(void); > > extern void rcu_irq_exit(void); > > +extern bool rcu_watching_this_cpu(void); > > > > #ifdef CONFIG_RCU_USER_QS > > extern void rcu_user_enter(void); > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index a06d172..7b8fcee 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -710,6 +710,18 @@ EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); > > #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */ > > > > /** > > + * rcu_watching_this_cpu - are RCU read-side critical sections safe? > > + * > > + * Return true if RCU is watching the running CPU, which means that this > > + * CPU can safely enter RCU read-side critical sections. The caller must > > + * have at least disabled preemption. > > + */ > > +bool rcu_watching_this_cpu(void) > > +{ > > + return !!__this_cpu_read(rcu_dynticks.dynticks_nesting); > > +} > > There is also rcu_is_cpu_idle().
Good point, thank you! I was clearly in autonomic-reflex mode yesterday. :-/
Here is the rcutree version:
int rcu_is_cpu_idle(void) { int ret;
preempt_disable(); ret = (atomic_read(&__get_cpu_var(rcu_dynticks).dynticks) & 0x1) == 0; preempt_enable(); return ret; }
And here is the rcutiny version:
int rcu_is_cpu_idle(void) { return !rcu_dynticks_nesting; }
Steve, could you please use rcu_is_cpu_idle()? I will revert yesterday's redundancy.
Thanx, Paul
> Thanks. > > > + > > +/** > > * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle > > * > > * If the current CPU is idle or running at a first-level (not nested) > > >
| |