From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
elver@google.com, dvyukov@google.com,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 11/12] rcu: Execute RCU reader shortly after rcu_core for strict GPs
Date: Wed, 12 Aug 2020 15:57:31 -0700 [thread overview]
Message-ID: <20200812225732.20068-11-paulmck@kernel.org> (raw)
In-Reply-To: <20200812225632.GA19759@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.org>
A kernel built with CONFIG_RCU_STRICT_GRACE_PERIOD=y needs a quiescent
state to appear very shortly after a CPU has noticed a new grace period.
Placing an RCU reader immediately after this point is ineffective because
this normally happens in softirq context, which acts as a big RCU reader.
This commit therefore introduces a new per-CPU work_struct, which is
used at the end of rcu_core() processing to schedule an RCU read-side
critical section from within a clean environment.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree.c | 13 +++++++++++++
kernel/rcu/tree.h | 1 +
2 files changed, 14 insertions(+)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index dd7af40..ac37343 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2634,6 +2634,14 @@ void rcu_force_quiescent_state(void)
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
+// Workqueue handler for an RCU reader for kernels enforcing struct RCU
+// grace periods.
+static void strict_work_handler(struct work_struct *work)
+{
+ rcu_read_lock();
+ rcu_read_unlock();
+}
+
/* Perform RCU core processing work for the current CPU. */
static __latent_entropy void rcu_core(void)
{
@@ -2678,6 +2686,10 @@ static __latent_entropy void rcu_core(void)
/* Do any needed deferred wakeups of rcuo kthreads. */
do_nocb_deferred_wakeup(rdp);
trace_rcu_utilization(TPS("End RCU core"));
+
+ // If strict GPs, schedule an RCU reader in a clean environment.
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+ queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work);
}
static void rcu_core_si(struct softirq_action *h)
@@ -3874,6 +3886,7 @@ rcu_boot_init_percpu_data(int cpu)
/* Set up local state, ensuring consistent view of global state. */
rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
+ INIT_WORK(&rdp->strict_work, strict_work_handler);
WARN_ON_ONCE(rdp->dynticks_nesting != 1);
WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)));
rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 309bc7f..e4f66b8 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -165,6 +165,7 @@ struct rcu_data {
/* period it is aware of. */
struct irq_work defer_qs_iw; /* Obtain later scheduler attention. */
bool defer_qs_iw_pending; /* Scheduler attention pending? */
+ struct work_struct strict_work; /* Schedule readers for strict GPs. */
/* 2) batch handling */
struct rcu_segcblist cblist; /* Segmented callback list, with */
--
2.9.5
next prev parent reply other threads:[~2020-08-12 22:57 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 22:56 [PATCH tip/core/rcu 0/12] Add strict short-grace-period Kconfig option Paul E. McKenney
2020-08-12 22:57 ` [PATCH tip/core/rcu 01/12] rcu: Add Kconfig option for strict RCU grace periods paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 02/12] rcu: Reduce leaf fanout " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 03/12] rcu: Restrict default jiffies_till_first_fqs for strict RCU GPs paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 04/12] rcu: Force DEFAULT_RCU_BLIMIT to 1000 " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 05/12] rcu: Always set .need_qs from __rcu_read_lock() for strict GPs paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 06/12] rcu: Do full report for .need_qs " paulmck
2020-08-13 0:50 ` Jann Horn
2020-08-13 3:29 ` Paul E. McKenney
2020-08-12 22:57 ` [PATCH tip/core/rcu 07/12] rcu: Attempt QS when CPU discovers GP " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 08/12] rcu: IPI all CPUs at GP start " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 09/12] rcu: IPI all CPUs at GP end " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 10/12] rcu: Provide optional RCU-reader exit delay " paulmck
2020-08-12 22:57 ` paulmck [this message]
2020-08-12 22:57 ` [PATCH tip/core/rcu 12/12] rcu: Report QS for outermost PREEMPT=n rcu_read_unlock() " paulmck
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