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    SubjectRe: [PATCH 2/2] locking/percpu-rwsem: Introduce bias knob
    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);
    +
    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;
    +}
    +
    +/**
    * rcu_sync_enter() - Force readers onto slowpath
    * @rsp: Pointer to rcu_sync structure to use for synchronization
    *
    \
     
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      Last update: 2016-07-14 22:01    [W:2.545 / U:1.120 seconds]
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