Messages in this thread Patch in this message | | | Date | Thu, 5 Sep 2013 19:40:05 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical section? |
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On Thu, 5 Sep 2013 14:05:37 -0700 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> > rcu: Is it safe to enter an RCU read-side critical section? > > 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,
Shouldn't that be a semi-colon?
"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.
s/the//
> > 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> > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 15d33d9..7c024fd 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -225,6 +225,9 @@ extern void rcu_idle_enter(void); > extern void rcu_idle_exit(void); > extern void rcu_irq_enter(void); > extern void rcu_irq_exit(void); > +#if defined(CONFIG_SMP) || defined(CONFIG_RCU_TRACE) > +extern bool rcu_watching_this_cpu(void);
I'm assuming that rcu is always watching a CPU if "!SMP" and "!RCU_TRACE". Thus you still need to have:
#else static inline bool rcu_watching_this_cpu(void) { return true; }
Otherwise we still fail to compile.
-- Steve
> +#endif /* #if defined(CONFIG_SMP) || defined(CONFIG_RCU_TRACE) */ > #ifdef CONFIG_RCU_USER_QS > extern void rcu_user_enter(void); > diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c > index 7e3b0d6..fce820f 100644 > --- a/kernel/rcutiny.c > +++ b/kernel/rcutiny.c > @@ -189,6 +189,17 @@ EXPORT_SYMBOL(rcu_is_cpu_idle); > > #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ > > +#ifdef CONFIG_RCU_TRACE > +/* > + * Test whether the current CPU can safely enter RCU read-side critical > + * sections. The caller must at least have disabled interrupts. > + */ > +bool rcu_watching_this_cpu(void) > +{ > + return !!rcu_dynticks_nesting; > +} > +#endif /* #ifdef CONFIG_RCU_TRACE */ > + > /* > * Test whether the current CPU was interrupted from idle. Nested > * interrupts don't count, we must be running at the first interrupt > 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); > +} > + > +/** > * 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)
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