From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E . McKenney" <paulmck@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Valentin Schneider <Valentin.Schneider@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Uladzislau Rezki <urezki@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Valentin Schneider <valentin.schneider@arm.com>,
Boqun Feng <boqun.feng@gmail.com>,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Josh Triplett <josh@joshtriplett.org>,
Joel Fernandes <joel@joelfernandes.org>,
rcu@vger.kernel.org
Subject: [PATCH 05/11] rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe
Date: Mon, 11 Oct 2021 16:51:34 +0200 [thread overview]
Message-ID: <20211011145140.359412-6-frederic@kernel.org> (raw)
In-Reply-To: <20211011145140.359412-1-frederic@kernel.org>
When callbacks are offloaded, the NOCB kthreads handle the callbacks
progression on behalf of rcu_core().
However during the (de-)offloading process, the kthread may not be
entirely up to the task. As a result some callbacks grace period
sequence number may remain stale for a while because rcu_core() won't
take care of them either.
Fix this with forcing callbacks acceleration from rcu_core() as long
as the offloading process isn't complete.
Reported-and-tested-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
kernel/rcu/tree.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4869a6856bf1..a43924244000 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2288,6 +2288,7 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
unsigned long flags;
unsigned long mask;
bool needwake = false;
+ bool needacc = false;
struct rcu_node *rnp;
WARN_ON_ONCE(rdp->cpu != smp_processor_id());
@@ -2315,16 +2316,29 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
* This GP can't end until cpu checks in, so all of our
* callbacks can be processed during the next GP.
*
- * NOCB kthreads have their own way to deal with that.
+ * NOCB kthreads have their own way to deal with that...
*/
- if (!rcu_rdp_is_offloaded(rdp))
+ if (!rcu_rdp_is_offloaded(rdp)) {
needwake = rcu_accelerate_cbs(rnp, rdp);
+ } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
+ /*
+ * ...but NOCB kthreads may miss or delay callbacks acceleration
+ * if in the middle of a (de-)offloading process.
+ */
+ needacc = true;
+ }
rcu_disable_urgency_upon_qs(rdp);
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
/* ^^^ Released rnp->lock */
if (needwake)
rcu_gp_kthread_wake();
+
+ if (needacc) {
+ rcu_nocb_lock_irqsave(rdp, flags);
+ rcu_accelerate_cbs_unlocked(rnp, rdp);
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ }
}
}
--
2.25.1
next prev parent reply other threads:[~2021-10-11 14:52 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-11 14:51 [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes v2 Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 01/11] rcu/nocb: Make local rcu_nocb_lock_irqsave() safe against concurrent deoffloading Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 02/11] rcu/nocb: Prepare state machine for a new step Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 03/11] rcu/nocb: Invoke rcu_core() at the start of deoffloading Frederic Weisbecker
2021-10-13 16:07 ` Boqun Feng
2021-10-14 11:07 ` Frederic Weisbecker
2021-10-14 11:42 ` Valentin Schneider
2021-10-14 13:57 ` Boqun Feng
2021-10-11 14:51 ` [PATCH 04/11] rcu/nocb: Make rcu_core() callbacks acceleration preempt-safe Frederic Weisbecker
2021-10-11 14:51 ` Frederic Weisbecker [this message]
2021-10-11 14:51 ` [PATCH 06/11] rcu/nocb: Check a stable offloaded state to manipulate qlen_last_fqs_check Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 07/11] rcu/nocb: Use appropriate rcu_nocb_lock_irqsave() Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 08/11] rcu/nocb: Limit number of softirq callbacks only on softirq Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 09/11] rcu: Fix callbacks processing time limit retaining cond_resched() Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 10/11] rcu: Apply callbacks processing time limit only on softirq Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 11/11] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread Frederic Weisbecker
2021-10-13 0:32 ` [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes v2 Paul E. McKenney
2021-10-13 3:28 ` Paul E. McKenney
2021-10-13 10:01 ` Frederic Weisbecker
2021-10-13 11:43 ` Frederic Weisbecker
2021-10-13 16:27 ` Paul E. McKenney
2021-10-14 10:43 ` Frederic Weisbecker
-- strict thread matches above, loose matches on Subject: below --
2021-09-29 22:10 [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 05/11] rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe Frederic Weisbecker
2021-10-01 17:50 ` Valentin Schneider
2021-10-04 13:14 ` Frederic Weisbecker
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