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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-05-30 10:11:24 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-07-22 15:26:58 -0700
commit24560056de61d86153cecb84d04e4237437f5888 (patch)
tree4674113128e446afb740fcc1d45d7fbd64dcff1f /kernel/rcu/tree.c
parentf765d1130700878c2275bc1ea09eed428f870a2a (diff)
downloadlinux-sh-24560056de61d86153cecb84d04e4237437f5888.tar.gz
rcu: Add RCU-sched flavors of get-state and cond-sync
The get_state_synchronize_rcu() and cond_synchronize_rcu() functions allow polling for grace-period completion, with an actual wait for a grace period occurring only when cond_synchronize_rcu() is called too soon after the corresponding get_state_synchronize_rcu(). However, these functions work only for vanilla RCU. This commit adds the get_state_synchronize_sched() and cond_synchronize_sched(), which provide the same capability for RCU-sched. Reported-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu/tree.c')
-rw-r--r--kernel/rcu/tree.c52
1 files changed, 52 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8b5dd8ba9495..9629298eea24 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3253,6 +3253,58 @@ void cond_synchronize_rcu(unsigned long oldstate)
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
+/**
+ * get_state_synchronize_sched - Snapshot current RCU-sched state
+ *
+ * Returns a cookie that is used by a later call to cond_synchronize_sched()
+ * to determine whether or not a full grace period has elapsed in the
+ * meantime.
+ */
+unsigned long get_state_synchronize_sched(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_sched()
+ * and cond_synchronize_sched().
+ */
+ return smp_load_acquire(&rcu_sched_state.gpnum);
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_sched);
+
+/**
+ * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
+ *
+ * @oldstate: return value from earlier call to get_state_synchronize_sched()
+ *
+ * If a full RCU-sched grace period has elapsed since the earlier call to
+ * get_state_synchronize_sched(), just return. Otherwise, invoke
+ * synchronize_sched() 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_sched(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_sched_state.completed);
+ if (ULONG_CMP_GE(oldstate, newstate))
+ synchronize_sched();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_sched);
+
static int synchronize_sched_expedited_cpu_stop(void *data)
{
/*