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>,
rcu <rcu@vger.kernel.org>, Uladzislau Rezki <urezki@gmail.com>,
Neeraj Upadhyay <quic_neeraju@quicinc.com>,
Boqun Feng <boqun.feng@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>
Subject: [PATCH 1/4] rcu/nocb: Protect lazy shrinker against concurrent (de-)offloading
Date: Wed, 22 Mar 2023 20:44:53 +0100 [thread overview]
Message-ID: <20230322194456.2331527-2-frederic@kernel.org> (raw)
In-Reply-To: <20230322194456.2331527-1-frederic@kernel.org>
The shrinker may run concurrently with callbacks (de-)offloading. As
such, calling rcu_nocb_lock() is very dangerous because it does a
conditional locking. The worst outcome is that rcu_nocb_lock() doesn't
lock but rcu_nocb_unlock() eventually unlocks, or the reverse, creating
an imbalance.
Fix this with protecting against (de-)offloading using the barrier mutex.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
kernel/rcu/tree_nocb.h | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index f2280616f9d5..dd9b655ae533 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1336,13 +1336,25 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
unsigned long flags;
unsigned long count = 0;
+ /*
+ * Protect against concurrent (de-)offloading. Otherwise nocb locking
+ * may be ignored or imbalanced.
+ */
+ mutex_lock(&rcu_state.barrier_mutex);
+
/* Snapshot count of all CPUs */
for_each_possible_cpu(cpu) {
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
- int _count = READ_ONCE(rdp->lazy_len);
+ int _count;
+
+ if (!rcu_rdp_is_offloaded(rdp))
+ continue;
+
+ _count = READ_ONCE(rdp->lazy_len);
if (_count == 0)
continue;
+
rcu_nocb_lock_irqsave(rdp, flags);
WRITE_ONCE(rdp->lazy_len, 0);
rcu_nocb_unlock_irqrestore(rdp, flags);
@@ -1352,6 +1364,9 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
if (sc->nr_to_scan <= 0)
break;
}
+
+ mutex_unlock(&rcu_state.barrier_mutex);
+
return count ? count : SHRINK_STOP;
}
--
2.34.1
next prev parent reply other threads:[~2023-03-22 19:45 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-22 19:44 [PATCH 0/4] rcu/nocb: Shrinker related boring fixes Frederic Weisbecker
2023-03-22 19:44 ` Frederic Weisbecker [this message]
2023-03-22 23:18 ` [PATCH 1/4] rcu/nocb: Protect lazy shrinker against concurrent (de-)offloading Paul E. McKenney
2023-03-24 0:55 ` Joel Fernandes
2023-03-24 1:06 ` Paul E. McKenney
2023-03-24 22:09 ` Frederic Weisbecker
2023-03-24 22:51 ` Paul E. McKenney
2023-03-26 20:01 ` Frederic Weisbecker
2023-03-26 21:45 ` Paul E. McKenney
2023-03-29 16:07 ` Frederic Weisbecker
2023-03-29 20:45 ` Paul E. McKenney
2023-03-22 19:44 ` [PATCH 2/4] rcu/nocb: Fix shrinker race against callback enqueuer Frederic Weisbecker
2023-03-22 23:19 ` Paul E. McKenney
2023-03-22 19:44 ` [PATCH 3/4] rcu/nocb: Recheck lazy callbacks under the ->nocb_lock from shrinker Frederic Weisbecker
2023-03-22 23:21 ` Paul E. McKenney
2023-03-22 19:44 ` [PATCH 4/4] rcu/nocb: Make shrinker to iterate only NOCB CPUs Frederic Weisbecker
2023-03-24 0:41 ` Joel Fernandes
2023-03-29 16:01 [PATCH 0/4 v2] rcu/nocb: Shrinker related boring fixes Frederic Weisbecker
2023-03-29 16:02 ` [PATCH 1/4] rcu/nocb: Protect lazy shrinker against concurrent (de-)offloading Frederic Weisbecker
2023-03-29 20:44 ` Paul E. McKenney
2023-03-29 21:18 ` Frederic Weisbecker
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