From: Boqun Feng <boqun.feng@gmail.com>
To: linux-kernel@vger.kernel.org, rcu@vger.kernel.org, lkmm@lists.linux.dev
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
Boqun Feng <boqun.feng@gmail.com>,
Waiman Long <longman@redhat.com>,
Davidlohr Bueso <dave@stgolabs.net>,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <neeraj.upadhyay@kernel.org>,
Joel Fernandes <joelagnelf@nvidia.com>,
Uladzislau Rezki <urezki@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang@linux.dev>, Breno Leitao <leitao@debian.org>,
aeh@meta.com, netdev@vger.kernel.org, edumazet@google.com,
jhs@mojatatu.com, kernel-team@meta.com,
Erik Lundgren <elundgren@meta.com>
Subject: [PATCH 8/8] locking/lockdep: Use shazptr to protect the key hashlist
Date: Tue, 24 Jun 2025 20:11:01 -0700 [thread overview]
Message-ID: <20250625031101.12555-9-boqun.feng@gmail.com> (raw)
In-Reply-To: <20250625031101.12555-1-boqun.feng@gmail.com>
Erik Lundgren and Breno Leitao reported [1] a case where
lockdep_unregister_key() can be called from time critical code pathes
where rntl_lock() may be held. And the synchronize_rcu() in it can slow
down operations such as using tc to replace a qdisc in a network device.
In fact the synchronize_rcu() in lockdep_unregister_key() is to wait for
all is_dynamic_key() callers to finish so that removing a key from the
key hashlist, and we can use shazptr to protect the hashlist as well.
Compared to the proposed solution which replaces synchronize_rcu() with
synchronize_rcu_expedited(), using shazptr here can achieve the
same/better synchronization time without the need to send IPI. Hence use
shazptr here.
Reported-by: Erik Lundgren <elundgren@meta.com>
Reported-by: Breno Leitao <leitao@debian.org>
Link: https://lore.kernel.org/all/20250321-lockdep-v1-1-78b732d195fb@debian.org/ [1]
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
kernel/locking/lockdep.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index dd2bbf73718b..5c205dd425f8 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -58,6 +58,7 @@
#include <linux/context_tracking.h>
#include <linux/console.h>
#include <linux/kasan.h>
+#include <linux/shazptr.h>
#include <asm/sections.h>
@@ -1267,14 +1268,18 @@ static bool is_dynamic_key(const struct lock_class_key *key)
hash_head = keyhashentry(key);
- rcu_read_lock();
+ /* Need preemption disable for using shazptr. */
+ guard(preempt)();
+
+ /* Protect the list search with shazptr. */
+ guard(shazptr)(hash_head);
+
hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
if (k == key) {
found = true;
break;
}
}
- rcu_read_unlock();
return found;
}
@@ -6620,7 +6625,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
/* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
- synchronize_rcu();
+ synchronize_shazptr(keyhashentry(key));
}
EXPORT_SYMBOL_GPL(lockdep_unregister_key);
--
2.39.5 (Apple Git-154)
next prev parent reply other threads:[~2025-06-25 3:11 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-25 3:10 [PATCH 0/8] Introduce simple hazard pointers for lockdep Boqun Feng
2025-06-25 3:10 ` [PATCH 1/8] Introduce simple hazard pointers Boqun Feng
2025-06-25 10:00 ` Peter Zijlstra
2025-06-25 14:25 ` Mathieu Desnoyers
2025-06-25 15:05 ` Boqun Feng
2025-06-25 15:52 ` Waiman Long
2025-06-25 16:09 ` Boqun Feng
2025-06-25 17:47 ` Waiman Long
2025-06-25 3:10 ` [PATCH 2/8] shazptr: Add refscale test Boqun Feng
2025-06-25 10:02 ` Peter Zijlstra
2025-06-25 3:10 ` [PATCH 3/8] shazptr: Add refscale test for wildcard Boqun Feng
2025-06-25 10:03 ` Peter Zijlstra
2025-06-25 3:10 ` [PATCH 4/8] shazptr: Avoid synchronize_shaptr() busy waiting Boqun Feng
2025-06-25 11:40 ` Peter Zijlstra
2025-06-25 11:56 ` Peter Zijlstra
2025-06-25 13:56 ` Frederic Weisbecker
2025-06-25 15:24 ` Boqun Feng
2025-06-26 13:45 ` Frederic Weisbecker
2025-06-25 3:10 ` [PATCH 5/8] shazptr: Allow skip self scan in synchronize_shaptr() Boqun Feng
2025-06-25 3:10 ` [PATCH 6/8] rcuscale: Allow rcu_scale_ops::get_gp_seq to be NULL Boqun Feng
2025-06-25 3:11 ` [PATCH 7/8] rcuscale: Add tests for simple hazard pointers Boqun Feng
2025-06-25 3:11 ` Boqun Feng [this message]
2025-06-25 11:59 ` [PATCH 8/8] locking/lockdep: Use shazptr to protect the key hashlist Peter Zijlstra
2025-06-25 14:18 ` Boqun Feng
2025-07-10 14:06 ` Breno Leitao
2025-07-11 2:31 ` Boqun Feng
2025-06-25 12:05 ` [PATCH 0/8] Introduce simple hazard pointers for lockdep Christoph Hellwig
2025-06-25 14:08 ` Boqun Feng
2025-06-26 10:16 ` Christoph Hellwig
2025-06-26 13:45 ` Mathieu Desnoyers
2025-06-26 15:47 ` Boqun Feng
2025-06-27 2:56 ` Paul E. McKenney
2025-06-25 12:25 ` Mathieu Desnoyers
2025-06-25 13:21 ` Boqun Feng
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