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-rw-r--r--kernel/rcu/tree.c62
1 files changed, 58 insertions, 4 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 351faba48b91..0c47e300210a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1421,13 +1421,14 @@ static int rcu_gp_init(struct rcu_state *rsp)
/* Advance to a new grace period and initialize state. */
record_gp_stall_check_time(rsp);
- smp_wmb(); /* Record GP times before starting GP. */
- rsp->gpnum++;
+ /* Record GP times before starting GP, hence smp_store_release(). */
+ smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
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! */
/*
* Set the quiescent-state-needed bits in all the rcu_node
@@ -1555,10 +1556,11 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
}
rnp = rcu_get_root(rsp);
raw_spin_lock_irq(&rnp->lock);
- smp_mb__after_unlock_lock();
+ smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
rcu_nocb_gp_set(rnp, nocb);
- rsp->completed = rsp->gpnum; /* Declare grace period done. */
+ /* Declare grace period done. */
+ ACCESS_ONCE(rsp->completed) = rsp->gpnum;
trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
rsp->fqs_state = RCU_GP_IDLE;
rdp = this_cpu_ptr(rsp->rda);
@@ -2637,6 +2639,58 @@ void synchronize_rcu_bh(void)
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
+/**
+ * get_state_synchronize_rcu - Snapshot current RCU state
+ *
+ * Returns a cookie that is used by a later call to cond_synchronize_rcu()
+ * to determine whether or not a full grace period has elapsed in the
+ * meantime.
+ */
+unsigned long get_state_synchronize_rcu(void)
+{
+ /*
+ * Any prior manipulation of RCU-protected data must happen
+ * before the load from ->gpnum.
+ */
+ smp_mb(); /* ^^^ */
+
+ /*
+ * Make sure this load happens before the purportedly
+ * time-consuming work between get_state_synchronize_rcu()
+ * and cond_synchronize_rcu().
+ */
+ return smp_load_acquire(&rcu_state->gpnum);
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
+
+/**
+ * cond_synchronize_rcu - Conditionally wait for an RCU grace period
+ *
+ * @oldstate: return value from earlier call to get_state_synchronize_rcu()
+ *
+ * If a full RCU grace period has elapsed since the earlier call to
+ * get_state_synchronize_rcu(), just return. Otherwise, invoke
+ * synchronize_rcu() to wait for a full grace period.
+ *
+ * Yes, this function does not take counter wrap into account. But
+ * counter wrap is harmless. If the counter wraps, we have waited for
+ * more than 2 billion grace periods (and way more on a 64-bit system!),
+ * so waiting for one additional grace period should be just fine.
+ */
+void cond_synchronize_rcu(unsigned long oldstate)
+{
+ unsigned long newstate;
+
+ /*
+ * Ensure that this load happens before any RCU-destructive
+ * actions the caller might carry out after we return.
+ */
+ newstate = smp_load_acquire(&rcu_state->completed);
+ if (ULONG_CMP_GE(oldstate, newstate))
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
+
static int synchronize_sched_expedited_cpu_stop(void *data)
{
/*