On Sun, May 02, 2021 at 09:34:30PM -0700, Michel Lespinasse wrote:
> On Sun, May 02, 2021 at 08:40:49PM -0700, Paul E. McKenney wrote:
> > @@ -634,6 +644,12 @@ do { \
> > * sections, invocation of the corresponding RCU callback is deferred
> > * until after the all the other CPUs exit their critical sections.
> > *
> > + * In recent kernels, synchronize_rcu() and call_rcu() also wait for
> > + * regions of code with preemption disabled, including regions of code
> > + * with interrupts or softirqs disabled. If your kernel is old enough
> > + * for synchronize_sched() to be defined, only code enclosed within
> > + * rcu_read_lock() and rcu_read_unlock() are guaranteed to be waited for.
> > + *
> > * Note, however, that RCU callbacks are permitted to run concurrently
> > * with new RCU read-side critical sections. One way that this can happen
> > * is via the following sequence of events: (1) CPU 0 enters an RCU
>
> You still have "old enough" / "recent kernels" here. But maybe it's OK
> given that you added relevant version numbers elsewhere.
>
> Everything else looks great to me.
Good point! Like this?
Thanx, Paul
------------------------------------------------------------------------
commit fd8393a2a8a5ffd25d0766abb262137c36bda9f3
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date: Mon May 3 09:32:14 2021 -0700
fixup! rcu: Improve comments describing RCU read-side critical sections
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 901ab6fa252b..323954363389 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -644,11 +644,11 @@ do { \
* sections, invocation of the corresponding RCU callback is deferred
* until after the all the other CPUs exit their critical sections.
*
- * In recent kernels, synchronize_rcu() and call_rcu() also wait for
- * regions of code with preemption disabled, including regions of code
- * with interrupts or softirqs disabled. If your kernel is old enough
- * for synchronize_sched() to be defined, only code enclosed within
- * rcu_read_lock() and rcu_read_unlock() are guaranteed to be waited for.
+ * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also
+ * wait for regions of code with preemption disabled, including regions of
+ * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which
+ * define synchronize_sched(), only code enclosed within rcu_read_lock()
+ * and rcu_read_unlock() are guaranteed to be waited for.
*
* Note, however, that RCU callbacks are permitted to run concurrently
* with new RCU read-side critical sections. One way that this can happen
