On 07/14, Peter Zijlstra wrote: > > On Thu, Jul 14, 2016 at 04:58:44PM +0200, Oleg Nesterov wrote: > > > > But note that we do not need RCU_NONE. All we need is the trivial change > > below. > > Hurm, maybe. So having that unbalanced keeps us in GP_PASSED state and > since we'll never drop gp_count back to 0 nothing will ever happen.
Yes, exactly. Of course, this is a bit ugly, I'll try to send some rcu-sync cleanups/simplifications later. Perhaps we can even add a "cgroup migration is not that cold as it was supposed" boot option for this rcu_sync_enter() for now, not sure. > > Damn, I am trying to find my old rcu-sync patches which I didn't > > send, but can't... OK, this almost off-topic right now, just this "enter" > > is ugly and we can't switch the slow/fast modes dynamically. > > > > The rest of you patch is "optimize the slow path" and we already discussed > > it before, I personally like it. Perhaps you can redo it without RCU_NONE > > part? > > Indeed, I rebased that patch on top of the current tree and had to add > support for down_trylock() but otherwise much the same thing. > > I can send it out again. Great, thanks! This should fix the problem. Oleg.