On Thu, Jan 21, 2021 at 04:20:12PM -0800, Paul E. McKenney wrote: > > --- > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index 368749008ae8..2c8d4c3e341e 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -445,7 +445,7 @@ static int rcu_is_cpu_rrupt_from_idle(void) > > /* > > * Usually called from the tick; but also used from smp_function_call() > > * for expedited grace periods. This latter can result in running from > > - * the idle task, instead of an actual IPI. > > + * a (usually the idle) task, instead of an actual IPI. > > The story is growing enough hair that we should tell it only once. > So here just where it is called from: > > /* > * Usually called from the tick; but also used from smp_function_call() > * for expedited grace periods. > */ > > > lockdep_assert_irqs_disabled(); > > > > @@ -461,9 +461,14 @@ static int rcu_is_cpu_rrupt_from_idle(void) > > return false; > > > > /* > > - * If we're not in an interrupt, we must be in the idle task! > > + * If we're not in an interrupt, we must be in task context. > > + * > > + * This will typically be the idle task through: > > + * flush_smp_call_function_from_idle(), > > + * > > + * but can also be in CPU HotPlug through smpcfd_dying(). > > */ > > Good, but how about like this? > > /* > * If we are not in an interrupt handler, we must be in > * smp_call_function() handler. > * > * Normally, smp_call_function() handlers are invoked from > * the idle task via flush_smp_call_function_from_idle(). > * However, they can also be invoked from CPU hotplug > * operations via smpcfd_dying(). > */ > > > - WARN_ON_ONCE(!nesting && !is_idle_task(current)); > > + WARN_ON_ONCE(!nesting && !in_task(current)); > > This is used in time-critical contexts, so why not RCU_LOCKDEP_WARN()? > That should also allow checking more closely. Would something like the > following work? > > RCU_LOCKDEP_WARN(!nesting && !is_idle_task(current) && > (!in_task(current) || !lockdep_cpus_write_held())); > > Where lockdep_cpus_write_held is defined in kernel/cpu.c:
Works for me, except s/in_task(current)/in_task()/ compiles a lot better.
