On Tue, Nov 19, 2019 at 09:21:49AM -0500, Steven Rostedt wrote: > On Tue, 19 Nov 2019 09:46:40 +0100 > Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > > On !RT a locked spinlock_t and rwlock_t disables preemption which > > implies a RCU read section. There is code that relies on that behaviour. > > > > Add an explicit RCU read section on RT while a sleeping lock (a lock > > which would disables preemption on !RT) acquired. > > I know that there was some work to merge the RCU flavors of > rcu_read_lock and rcu_read_lock_sched, I'm assuming this depends on > that behavior. That is, a synchronize_rcu() will wait for all CPUs to > schedule and all grace periods to finish, which means that those using s/grace periods/RCU readers/, but yes. > rcu_read_lock() and those using all CPUs to schedule can be > interchangeable. That is, on !RT, it's likely that rcu_read_lock() > waiters will end up waiting for all CPUs to schedule, and on RT, this > makes it where those waiting for all CPUs to schedule, will also wait > for all rcu_read_lock()s grace periods to finish. If that's the case, > then this change is fine. But it depends on that being the case, which > it wasn't in older kernels, and we need to be careful about backporting > this. Right in one. Backporting across the RCU flavor consolidation change must be done with care. Thanx, Paul
