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,
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,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <neeraju@codeaurora.org>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 08/21] rcu/nocb: Shutdown nocb timer on de-offloading
Date: Tue, 5 Jan 2021 20:48:40 -0800 [thread overview]
Message-ID: <20210106044853.20812-8-paulmck@kernel.org> (raw)
In-Reply-To: <20210106013950.GA14663@paulmck-ThinkPad-P72>
From: Frederic Weisbecker <frederic@kernel.org>
This commit ensures that the nocb timer is shut down before reaching the
final de-offloaded state. The key goal is to prevent the timer handler
from manipulating the callbacks without the protection of the nocb locks.
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Inspired-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree.h | 1 +
kernel/rcu/tree_plugin.h | 12 +++++++++++-
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index e0deb48..5d359b9 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -257,6 +257,7 @@ struct rcu_data {
};
/* Values for nocb_defer_wakeup field in struct rcu_data. */
+#define RCU_NOCB_WAKE_OFF -1
#define RCU_NOCB_WAKE_NOT 0
#define RCU_NOCB_WAKE 1
#define RCU_NOCB_WAKE_FORCE 2
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 03ae1ce..c88ad62 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1665,6 +1665,8 @@ static void wake_nocb_gp(struct rcu_data *rdp, bool force,
static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
const char *reason)
{
+ if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_OFF)
+ return;
if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
mod_timer(&rdp->nocb_timer, jiffies + 1);
if (rdp->nocb_defer_wakeup < waketype)
@@ -2243,7 +2245,7 @@ static int rcu_nocb_cb_kthread(void *arg)
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
{
- return READ_ONCE(rdp->nocb_defer_wakeup);
+ return READ_ONCE(rdp->nocb_defer_wakeup) > RCU_NOCB_WAKE_NOT;
}
/* Do a deferred wakeup of rcu_nocb_kthread(). */
@@ -2337,6 +2339,12 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
swait_event_exclusive(rdp->nocb_state_wq,
!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB |
SEGCBLIST_KTHREAD_GP));
+ /* Make sure nocb timer won't stay around */
+ rcu_nocb_lock_irqsave(rdp, flags);
+ WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_OFF);
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ del_timer_sync(&rdp->nocb_timer);
+
return ret;
}
@@ -2394,6 +2402,8 @@ static int __rcu_nocb_rdp_offload(struct rcu_data *rdp)
* SEGCBLIST_SOFTIRQ_ONLY mode.
*/
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+ /* Re-enable nocb timer */
+ WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
/*
* We didn't take the nocb lock while working on the
* rdp->cblist in SEGCBLIST_SOFTIRQ_ONLY mode.
--
2.9.5
next prev parent reply other threads:[~2021-01-06 4:51 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-06 1:39 [PATCH tip/core/rcu 0/21] Provide runtime switching of offloaded CPUs Paul E. McKenney
2021-01-06 4:48 ` [PATCH tip/core/rcu 01/21] rcu/nocb: Turn enabled/offload states into a common flag paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 02/21] rcu/nocb: Provide basic callback offloading state machine bits paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 03/21] rcu/nocb: Always init segcblist on CPU up paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 04/21] rcu/nocb: De-offloading CB kthread paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 05/21] rcu/nocb: Don't deoffload an offline CPU with pending work paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 06/21] rcu/nocb: De-offloading GP kthread paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 07/21] rcu/nocb: Re-offload support paulmck
2021-01-06 4:48 ` paulmck [this message]
2021-01-06 4:48 ` [PATCH tip/core/rcu 09/21] rcu/nocb: Flush bypass before setting SEGCBLIST_SOFTIRQ_ONLY paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 10/21] rcu/nocb: Set SEGCBLIST_SOFTIRQ_ONLY at the very last stage of de-offloading paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 11/21] rcu/nocb: Only cond_resched() from actual offloaded batch processing paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 12/21] rcu/nocb: Process batch locally as long as offloading isn't complete paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 13/21] rcu/nocb: Locally accelerate callbacks " paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 14/21] cpu/hotplug: Add lockdep_is_cpus_held() paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 15/21] timer: Add timer_curr_running() paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 16/21] rcutorture: Test runtime toggling of CPUs' callback offloading paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 17/21] tools/rcutorture: Support nocb toggle in TREE01 paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 18/21] rcu/nocb: Add grace period and task state to show_rcu_nocb_state() output paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 19/21] rcu/nocb: Add nocb CB kthread list " paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 20/21] rcu/nocb: Code-style nits in callback-offloading toggling paulmck
2021-01-06 4:48 ` [PATCH tip/core/rcu 21/21] rcu: Do any deferred nocb wakeups at CPU offline time paulmck
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