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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>,
	Boqun Feng <boqun.feng@gmail.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Neeraj Upadhyay <neeraju@codeaurora.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Stable <stable@vger.kernel.org>,
	Joel Fernandes <joel@joelfernandes.org>
Subject: [PATCH 01/16] rcu/nocb: Fix potential missed nocb_timer rearm
Date: Thu, 28 Jan 2021 18:12:07 +0100	[thread overview]
Message-ID: <20210128171222.131380-2-frederic@kernel.org> (raw)
In-Reply-To: <20210128171222.131380-1-frederic@kernel.org>

The "nocb_bypass_timer" ends up calling wake_nocb_gp() which deletes
the pending "nocb_timer" (note they are not the same timers) for the
given rdp without resetting the matching state stored in nocb_defer
wakeup.

As a result, a future call_rcu() on that rdp may be fooled and think the
timer is armed when it's not, missing a deferred nocb_gp wakeup.

Fix this with resetting rdp->nocb_defer_wakeup when we disarm the timer.

Fixes: d1b222c6be1f (rcu/nocb: Add bypass callback queueing)
Cc: Stable <stable@vger.kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/rcu/tree_plugin.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 7e33dae0e6ee..a44f80d7661b 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1705,6 +1705,8 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force,
 		rcu_nocb_unlock_irqrestore(rdp, flags);
 		return false;
 	}
+
+	rdp->nocb_defer_wakeup = RCU_NOCB_WAKE_NOT;
 	del_timer(&rdp->nocb_timer);
 	rcu_nocb_unlock_irqrestore(rdp, flags);
 	raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
-- 
2.25.1


  reply	other threads:[~2021-01-28 17:45 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-28 17:12 [PATCH 00/16] rcu/nocb updates Frederic Weisbecker
2021-01-28 17:12 ` Frederic Weisbecker [this message]
     [not found]   ` <20210128184834.GP2743@paulmck-ThinkPad-P72>
2021-01-28 21:23     ` [PATCH 01/16] rcu/nocb: Fix potential missed nocb_timer rearm Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 02/16] rcu/nocb: Comment the reason behind BH disablement on batch processing Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 03/16] rcu/nocb: Forbid NOCB toggling on offline CPUs Frederic Weisbecker
2021-01-28 19:52   ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 04/16] rcu/nocb: Only (re-)initialize segcblist when needed on CPU up Frederic Weisbecker
     [not found]   ` <20210128191228.GQ2743@paulmck-ThinkPad-P72>
2021-01-28 21:34     ` Frederic Weisbecker
2021-01-28 21:45       ` Paul E. McKenney
2021-01-29  0:26         ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 05/16] rcu/nocb: Disable bypass when CPU isn't completely offloaded Frederic Weisbecker
2021-01-28 21:31   ` Paul E. McKenney
2021-01-28 22:25     ` Frederic Weisbecker
2021-01-29  0:19       ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 06/16] rcu/nocb: Avoid confusing double write of rdp->nocb_cb_sleep Frederic Weisbecker
2021-01-28 21:42   ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 07/16] rcu/nocb: Rename nocb_gp_update_state to nocb_gp_update_state_deoffloading Frederic Weisbecker
2021-01-29  0:49   ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 08/16] rcu/nocb: Move trace_rcu_nocb_wake() calls outside nocb_lock when possible Frederic Weisbecker
2021-01-29  0:51   ` Paul E. McKenney
2021-01-28 17:12 ` [PATCH 09/16] rcu/nocb: Merge nocb_timer to the rdp leader Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 10/16] rcu/nocb: Directly call __wake_nocb_gp() from bypass timer Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 11/16] rcu/nocb: Allow de-offloading rdp leader Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 12/16] rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 13/16] rcu/nocb: Delete bypass_timer " Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 14/16] rcu/nocb: Only cancel nocb timer if not polling Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 15/16] rcu/nocb: Prepare for finegrained deferred wakeup Frederic Weisbecker
2021-01-28 17:12 ` [PATCH 16/16] rcu/nocb: Unify timers Frederic Weisbecker

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