From: "tip-bot2 for Paul E. McKenney" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Frederic Weisbecker <frederic@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: core/rcu] rcu: Provide polling interfaces for Tiny RCU grace periods
Date: Sun, 11 Apr 2021 13:43:18 -0000 [thread overview]
Message-ID: <161814859843.29796.8740406362665343747.tip-bot2@tip-bot2> (raw)
The following commit has been merged into the core/rcu branch of tip:
Commit-ID: 0909fc2b2c41aae50a18a36ac2858d156f521871
Gitweb: https://git.kernel.org/tip/0909fc2b2c41aae50a18a36ac2858d156f521871
Author: Paul E. McKenney <paulmck@kernel.org>
AuthorDate: Thu, 25 Feb 2021 17:36:06 -08:00
Committer: Paul E. McKenney <paulmck@kernel.org>
CommitterDate: Wed, 24 Mar 2021 17:16:15 -07:00
rcu: Provide polling interfaces for Tiny RCU grace periods
There is a need for a non-blocking polling interface for RCU grace
periods, so this commit supplies start_poll_synchronize_rcu() and
poll_state_synchronize_rcu() for this purpose. Note that the existing
get_state_synchronize_rcu() may be used if future grace periods are
inevitable (perhaps due to a later call_rcu() invocation). The new
start_poll_synchronize_rcu() is to be used if future grace periods
might not otherwise happen. Finally, poll_state_synchronize_rcu()
provides a lockless check for a grace period having elapsed since
the corresponding call to either of the get_state_synchronize_rcu()
or start_poll_synchronize_rcu().
As with get_state_synchronize_rcu(), the return value from either
get_state_synchronize_rcu() or start_poll_synchronize_rcu() is passed in
to a later call to either poll_state_synchronize_rcu() or the existing
(might_sleep) cond_synchronize_rcu().
[ paulmck: Revert cond_synchronize_rcu() to might_sleep() per Frederic Weisbecker feedback. ]
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
include/linux/rcutiny.h | 7 +++----
kernel/rcu/tiny.c | 40 ++++++++++++++++++++++++++++++++++++++++-
2 files changed, 43 insertions(+), 4 deletions(-)
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 2a97334..35e0be3 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -17,10 +17,9 @@
/* Never flag non-existent other CPUs! */
static inline bool rcu_eqs_special_set(int cpu) { return false; }
-static inline unsigned long get_state_synchronize_rcu(void)
-{
- return 0;
-}
+unsigned long get_state_synchronize_rcu(void);
+unsigned long start_poll_synchronize_rcu(void);
+bool poll_state_synchronize_rcu(unsigned long oldstate);
static inline void cond_synchronize_rcu(unsigned long oldstate)
{
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index aa897c3..c8a029f 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -32,12 +32,14 @@ struct rcu_ctrlblk {
struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
struct rcu_head **curtail; /* ->next pointer of last CB. */
+ unsigned long gp_seq; /* Grace-period counter. */
};
/* Definition for rcupdate control block. */
static struct rcu_ctrlblk rcu_ctrlblk = {
.donetail = &rcu_ctrlblk.rcucblist,
.curtail = &rcu_ctrlblk.rcucblist,
+ .gp_seq = 0 - 300UL,
};
void rcu_barrier(void)
@@ -56,6 +58,7 @@ void rcu_qs(void)
rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
raise_softirq_irqoff(RCU_SOFTIRQ);
}
+ WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 1);
local_irq_restore(flags);
}
@@ -177,6 +180,43 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
}
EXPORT_SYMBOL_GPL(call_rcu);
+/*
+ * Return a grace-period-counter "cookie". For more information,
+ * see the Tree RCU header comment.
+ */
+unsigned long get_state_synchronize_rcu(void)
+{
+ return READ_ONCE(rcu_ctrlblk.gp_seq);
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
+
+/*
+ * Return a grace-period-counter "cookie" and ensure that a future grace
+ * period completes. For more information, see the Tree RCU header comment.
+ */
+unsigned long start_poll_synchronize_rcu(void)
+{
+ unsigned long gp_seq = get_state_synchronize_rcu();
+
+ if (unlikely(is_idle_task(current))) {
+ /* force scheduling for rcu_qs() */
+ resched_cpu(0);
+ }
+ return gp_seq;
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
+
+/*
+ * Return true if the grace period corresponding to oldstate has completed
+ * and false otherwise. For more information, see the Tree RCU header
+ * comment.
+ */
+bool poll_state_synchronize_rcu(unsigned long oldstate)
+{
+ return READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate;
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
+
void __init rcu_init(void)
{
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
reply other threads:[~2021-04-11 13:44 UTC|newest]
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