On Thu, Jul 14, 2016 at 09:20:18PM +0200, Peter Zijlstra wrote: > On Thu, Jul 14, 2016 at 08:43:51PM +0200, Oleg Nesterov wrote: > > > > Oh well... I personally do not think this is what we want... Can't > > we just add the stupid rcu_sync_enter() into cgroup_init() at least > > for now? Yes, this means the unnecessary .sync() at boot time, but > > it will go away after cleanups I am going to send. > > Something like so then? > > --- > --- a/include/linux/rcu_sync.h > +++ b/include/linux/rcu_sync.h > @@ -59,6 +59,7 @@ static inline bool rcu_sync_is_idle(stru > } > > extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type); > +extern void rcu_sync_sabotage(struct rcu_sync *); > extern void rcu_sync_enter(struct rcu_sync *); > extern void rcu_sync_exit(struct rcu_sync *); > extern void rcu_sync_dtor(struct rcu_sync *); > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -5609,6 +5609,8 @@ int __init cgroup_init(void) > BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files)); > BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files)); > > + rcu_sync_sabotage(&cgroup_threadgroup_rwsem.rss);
With a name like that... > + > get_user_ns(init_cgroup_ns.user_ns); > > mutex_lock(&cgroup_mutex); > --- a/kernel/rcu/sync.c > +++ b/kernel/rcu/sync.c > @@ -83,6 +83,21 @@ void rcu_sync_init(struct rcu_sync *rsp, > } > > /** > + * rcu_sync_sabotage() - Sabotage a fresh rcu_sync instance > + * @rsp: Pointer to rcu_sync structure to be sabotaged > + * > + * Must be called after rcu_sync_init() and before first use. > + * > + * Ensures rcu_sync_is_idle() returns false and rcu_sync_{enter,exit}() pairs > + * turn into NO-OPs. > + */ > +void rcu_sync_sabotage(struct rcu_sync *rsp) > +{ > + rsp->gp_count++; > + rsp->gp_state = !GP_IDLE; ??? A very strange way to say GP_PENDING. A new GP_DISABLED, perhaps? Thanx, Paul > +} > + > +/** > * rcu_sync_enter() - Force readers onto slowpath > * @rsp: Pointer to rcu_sync structure to use for synchronization > * >