[PATCH tip/core/rcu 16/20] rcu: Eliminate ->onoff_mutex from rcu_node structure

Paul E. McKenney
2015-03-03T17:44:16Z

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>
---
kernel/rcu/tree.c | 15 ---------------
kernel/rcu/tree.h | 2 --
2 files changed, 17 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f0f4d3510d24..79d53399247e 100644
--- 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 aa42562ff5b2..a69d3dab2ec4 100644
--- 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. */
--
1.8.1.5