On Fri, Jul 12, 2019 at 04:32:06PM -0700, Paul E. McKenney wrote: > On Fri, Jul 12, 2019 at 05:35:59PM -0400, Joel Fernandes wrote: > > On Fri, Jul 12, 2019 at 01:00:18PM -0400, Joel Fernandes (Google) wrote: > > > The rcu/sync code was doing its own check whether we are in a reader > > > section. With RCU consolidating flavors and the generic helper added in > > > this series, this is no longer need. We can just use the generic helper > > > and it results in a nice cleanup. > > > > > > Cc: Oleg Nesterov <oleg@xxxxxxxxxx> > > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > > > Hi Oleg, > > Slightly unrelated to the patch, > > I tried hard to understand this comment below in percpu_down_read() but no dice. > > > > I do understand how rcu sync and percpu rwsem works, however the comment > > below didn't make much sense to me. For one, there's no readers_fast anymore > > so I did not follow what readers_fast means. Could the comment be updated to > > reflect latest changes? > > Also could you help understand how is a writer not able to change > > sem->state and count the per-cpu read counters at the same time as the > > comment tries to say? > > > > /* > > * We are in an RCU-sched read-side critical section, so the writer > > * cannot both change sem->state from readers_fast and start checking > > * counters while we are here. So if we see !sem->state, we know that > > * the writer won't be checking until we're past the preempt_enable() > > * and that once the synchronize_rcu() is done, the writer will see > > * anything we did within this RCU-sched read-size critical section. > > */ > > > > Also, > > I guess we could get rid of all of the gp_ops struct stuff now that since all > > the callbacks are the same now. I will post that as a follow-up patch to this > > series. > > Hello, Joel, > > Oleg has a set of patches updating this code that just hit mainline > this week. These patches get rid of the code that previously handled > RCU's multiple flavors. Or are you looking at current mainline and > me just missing your point? > Hi Paul, You are right on point. I have a bad habit of not rebasing my trees. In this case the feature branch of mine in concern was based on v5.1. Needless to say, I need to rebase my tree. Yes, this sync clean up patch does conflict when I rebase, but other patches rebase just fine. The 2 options I see are: 1. Let us drop this patch for now and I resend it later. 2. I resend all patches based on Linus's master branch. thanks, - Joel
