From: "Paul E. McKenney" <paulmck@kernel.org>
To: Zqiang <qiang1.zhang@intel.com>
Cc: frederic@kernel.org, quic_neeraju@quicinc.com,
joel@joelfernandes.org, rcu@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] rcu: Remove impossible wakeup rcu GP kthread action from rcu_report_qs_rdp()
Date: Wed, 18 Jan 2023 10:07:14 -0800 [thread overview]
Message-ID: <20230118180714.GD2948950@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <20230118073014.2020743-1-qiang1.zhang@intel.com>
On Wed, Jan 18, 2023 at 03:30:14PM +0800, Zqiang wrote:
> When inovke rcu_report_qs_rdp(), if current CPU's rcu_data structure's ->
> grpmask has not been cleared from the corresponding rcu_node structure's
> ->qsmask, after that will clear and report quiescent state, but in this
> time, this also means that current grace period is not end, the current
> grace period is ongoing, because the rcu_gp_in_progress() currently return
> true, so for non-offloaded rdp, invoke rcu_accelerate_cbs() is impossible
> to return true.
>
> This commit therefore remove impossible rcu_gp_kthread_wake() calling.
>
> Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Queued (wordsmithed as shown below, as always, please check) for further
testing and review, thank you both!
Thanx, Paul
------------------------------------------------------------------------
commit fbe3e300ec8b3edd2b8f84dab4dc98947cf71eb8
Author: Zqiang <qiang1.zhang@intel.com>
Date: Wed Jan 18 15:30:14 2023 +0800
rcu: Remove never-set needwake assignment from rcu_report_qs_rdp()
The rcu_accelerate_cbs() function is invoked by rcu_report_qs_rdp()
only if there is a grace period in progress that is still blocked
by at least one CPU on this rcu_node structure. This means that
rcu_accelerate_cbs() should never return the value true, and thus that
this function should never set the needwake variable and in turn never
invoke rcu_gp_kthread_wake().
This commit therefore removes the needwake variable and the invocation
of rcu_gp_kthread_wake() in favor of a WARN_ON_ONCE() on the call to
rcu_accelerate_cbs(). The purpose of this new WARN_ON_ONCE() is to
detect situations where the system's opinion differs from ours.
Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b2c2045294780..7a3085ad0a7df 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1956,7 +1956,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
{
unsigned long flags;
unsigned long mask;
- bool needwake = false;
bool needacc = false;
struct rcu_node *rnp;
@@ -1988,7 +1987,12 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
* NOCB kthreads have their own way to deal with that...
*/
if (!rcu_rdp_is_offloaded(rdp)) {
- needwake = rcu_accelerate_cbs(rnp, rdp);
+ /*
+ * The current GP has not yet ended, so it
+ * should not be possible for rcu_accelerate_cbs()
+ * to return true. So complain, but don't awaken.
+ */
+ WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp));
} else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
/*
* ...but NOCB kthreads may miss or delay callbacks acceleration
@@ -2000,8 +2004,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
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);
next prev parent reply other threads:[~2023-01-18 18:08 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-18 7:30 [PATCH v3] rcu: Remove impossible wakeup rcu GP kthread action from rcu_report_qs_rdp() Zqiang
2023-01-18 10:18 ` Frederic Weisbecker
2023-01-18 18:07 ` Paul E. McKenney [this message]
2023-01-18 23:30 ` Zhang, Qiang1
2023-01-20 3:14 ` Joel Fernandes
2023-01-20 3:17 ` Joel Fernandes
2023-01-20 4:09 ` Zhang, Qiang1
2023-01-20 4:40 ` Joel Fernandes
2023-01-20 8:19 ` Zhang, Qiang1
2023-01-20 13:27 ` Joel Fernandes
2023-01-20 20:33 ` Paul E. McKenney
2023-01-20 22:35 ` Frederic Weisbecker
2023-01-20 23:20 ` Paul E. McKenney
2023-01-20 23:04 ` Frederic Weisbecker
2023-01-23 15:22 ` Joel Fernandes
2023-01-23 16:27 ` Frederic Weisbecker
2023-01-23 20:54 ` Joel Fernandes
2023-01-23 21:11 ` Frederic Weisbecker
2023-01-24 16:58 ` Joel Fernandes
2023-01-21 0:38 ` Zhang, Qiang1
2023-01-24 17:10 ` Joel Fernandes
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