rcu: Eliminate ->onoff_mutex from rcu_node structure

Because that RCU grace-period initialization need no longer exclude
CPU-hotplug operations, this commit eliminates the ->onoff_mutex and
its uses.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f0f4d35..79d5339 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -101,7 +101,6 @@ struct rcu_state sname##_state = { \
        .orphan_nxttail = &sname##_state.orphan_nxtlist, \
        .orphan_donetail = &sname##_state.orphan_donelist, \
        .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
-       .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
        .name = RCU_STATE_NAME(sname), \
        .abbr = sabbr, \
 }; \
@@ -1754,10 +1753,6 @@ static int rcu_gp_init(struct rcu_state *rsp)
        trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
        raw_spin_unlock_irq(&rnp->lock);
 
-       /* Exclude any concurrent CPU-hotplug operations. */
-       mutex_lock(&rsp->onoff_mutex);
-       smp_mb__after_unlock_lock(); /* ->gpnum increment before GP! */
-
        /*
         * Apply per-leaf buffered online and offline operations to the
         * rcu_node tree.  Note that this new grace period need not wait
@@ -1844,7 +1839,6 @@ static int rcu_gp_init(struct rcu_state *rsp)
                        schedule_timeout_uninterruptible(gp_init_delay);
        }
 
-       mutex_unlock(&rsp->onoff_mutex);
        return 1;
 }
 
@@ -2498,9 +2492,6 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
        /* Adjust any no-longer-needed kthreads. */
        rcu_boost_kthread_setaffinity(rnp, -1);
 
-       /* Exclude any attempts to start a new grace period. */
-       mutex_lock(&rsp->onoff_mutex);
-
        /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
        raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
        rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
@@ -2517,7 +2508,6 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
        WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
                  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
                  cpu, rdp->qlen, rdp->nxtlist);
-       mutex_unlock(&rsp->onoff_mutex);
 }
 
 #else /* #ifdef CONFIG_HOTPLUG_CPU */
@@ -3700,9 +3690,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
        struct rcu_node *rnp = rcu_get_root(rsp);
 
-       /* Exclude new grace periods. */
-       mutex_lock(&rsp->onoff_mutex);
-
        /* Set up local state, ensuring consistent view of global state. */
        raw_spin_lock_irqsave(&rnp->lock, flags);
        rdp->beenonline = 1;     /* We have now been online. */
@@ -3733,8 +3720,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
        rdp->qs_pending = false;
        trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
-
-       mutex_unlock(&rsp->onoff_mutex);
 }
 
 static void rcu_prepare_cpu(int cpu)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index aa42562..a69d3da 100644 (file)
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -456,8 +456,6 @@ struct rcu_state {
        long qlen;                              /* Total number of callbacks. */
        /* End of fields guarded by orphan_lock. */
 
-       struct mutex onoff_mutex;               /* Coordinate hotplug & GPs. */
-
        struct mutex barrier_mutex;             /* Guards barrier fields. */
        atomic_t barrier_cpu_count;             /* # CPUs waiting on. */
        struct completion barrier_completion;   /* Wake at barrier end. */