On Fri, Aug 23, 2019 at 02:28:46PM -0500, Scott Wood wrote: > On Fri, 2019-08-23 at 18:20 +0200, Sebastian Andrzej Siewior wrote: > > On 2019-08-21 18:19:05 [-0500], Scott Wood wrote: > > > Without this, rcu_note_context_switch() will complain if an RCU read > > > lock is held when migrate_enable() calls stop_one_cpu(). > > > > > > Signed-off-by: Scott Wood <swood@xxxxxxxxxx> > > > --- > > > v2: Added comment. > > > > > > If my migrate disable changes aren't taken, then pin_current_cpu() > > > will also need to use sleeping_lock_inc() because calling > > > __read_rt_lock() bypasses the usual place it's done. > > > > > > include/linux/sched.h | 4 ++-- > > > kernel/rcu/tree_plugin.h | 2 +- > > > kernel/sched/core.c | 8 ++++++++ > > > 3 files changed, 11 insertions(+), 3 deletions(-) > > > > > > --- a/kernel/sched/core.c > > > +++ b/kernel/sched/core.c > > > @@ -7405,7 +7405,15 @@ void migrate_enable(void) > > > unpin_current_cpu(); > > > preempt_lazy_enable(); > > > preempt_enable(); > > > + > > > + /* > > > + * sleeping_lock_inc suppresses a debug check for > > > + * sleeping inside an RCU read side critical section > > > + */ > > > + sleeping_lock_inc(); > > > stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg); > > > + sleeping_lock_dec(); > > > > this looks like an ugly hack. This sleeping_lock_inc() is used where we > > actually hold a sleeping lock and schedule() which is okay. But this > > would mean we hold a RCU lock and schedule() anyway. Is that okay? > > Perhaps the name should be changed, but the concept is the same -- RT- > specific sleeping which should be considered involuntary for the purpose of > debug checks. Voluntary sleeping is not allowed in an RCU critical section > because it will break the critical section on certain flavors of RCU, but > that doesn't apply to the flavor used on RT. Sleeping for a long time in an > RCU critical section would also be a bad thing, but that also doesn't apply > here. I think the name should definitely be changed. At best, it is super confusing to call it "sleeping_lock" for this scenario. In fact here, you are not even blocking on a lock. Maybe "sleeping_allowed" or some such. thanks, - Joel
