linux-kernel - [PATCH RFC v2 tip/core/rcu 06/22] rcu: Reinstate synchronize_rcu

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Message-Id: <20200319001100.24917-6-paulmck@kernel.org>
Date:   Wed, 18 Mar 2020 17:10:44 -0700
From:   paulmck@...nel.org
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH RFC v2 tip/core/rcu 06/22] rcu: Reinstate synchronize_rcu_mult()

From: "Paul E. McKenney" <paulmck@...nel.org>

With the advent and likely usage of synchronize_rcu_rude(), there is
again a need to wait on multiple types of RCU grace periods, for
example, call_rcu_tasks() and call_rcu_tasks_rude().  This commit
therefore reinstates synchronize_rcu_mult() in order to allow these
grace periods to be straightforwardly waited on concurrently.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 include/linux/rcupdate_wait.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
index c0578ba..699b938 100644
--- a/include/linux/rcupdate_wait.h
+++ b/include/linux/rcupdate_wait.h
@@ -31,4 +31,23 @@ do {									\
 
 #define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
 
+/**
+ * synchronize_rcu_mult - Wait concurrently for multiple grace periods
+ * @...: List of call_rcu() functions for different grace periods to wait on
+ *
+ * This macro waits concurrently for multiple types of RCU grace periods.
+ * For example, synchronize_rcu_mult(call_rcu, call_rcu_tasks) would wait
+ * on concurrent RCU and RCU-tasks grace periods.  Waiting on a given SRCU
+ * domain requires you to write a wrapper function for that SRCU domain's
+ * call_srcu() function, with this wrapper supplying the pointer to the
+ * corresponding srcu_struct.
+ *
+ * The first argument tells Tiny RCU's _wait_rcu_gp() not to
+ * bother waiting for RCU.  The reason for this is because anywhere
+ * synchronize_rcu_mult() can be called is automatically already a full
+ * grace period.
+ */
+#define synchronize_rcu_mult(...) \
+	_wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)
+
 #endif /* _LINUX_SCHED_RCUPDATE_WAIT_H */
-- 
2.9.5