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bh=Qaq6Ozvd9kYKHAhw7AWsnmpFQIyCiRHSkKSayY7g9aE=; b=CZKp55MNNZRdjBr+KeZSGkLfqbXT1O3UTcr47koY9vnYbHcqTuCJ3uUT1Bsyfw+azlCqPd dWCRaOL8ZZH3aZJLZ6mMaLPptKlJXEPwyHrYcBeZwKn6HfyDF1MVjNN+1FqV/hd97/+cpF 0tVqjm2HxPgREZMYM/L3M+pFyqRStGdjiSC4rYiLUo4dryO4JwICeD6JRobY5XTmWTdNHB mj9bJSBmPtCiICiYVhUSia7Z5hCeOXOwrfO7roWE7c769Ng0DoZ9K5cn+TWFNAAKdnD2kv O80IZpRtdDBsaaf1WL5Lzeunr9VRwaYNmqDKrJ5HZiMyfaBF7XFTqQWHBvI7BQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1788334379; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Qaq6Ozvd9kYKHAhw7AWsnmpFQIyCiRHSkKSayY7g9aE=; b=H0QubGNLhOJdJmBLRSClHg7n0aTvOERqJK6YbAGxxpsWH0C26heUwmZNFgqLN/jqo1QegE V60Yo68Sg17cb5CA== From: "tip-bot2 for Eric Dumazet" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/urgent] locking/lockdep: Invalidate stale class_cache entries for zapped classes Cc: syzbot+2d770620059281e225a4@syzkaller.appspotmail.com, Eric Dumazet , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20260824155129.676096-1-edumazet@google.com> References: <20260824155129.676096-1-edumazet@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <178833437727.3717435.4595107264514888193.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the locking/urgent branch of tip: Commit-ID: 02c6be7d675b21d81f0ba3a524346850a8c0e3bf Gitweb: https://git.kernel.org/tip/02c6be7d675b21d81f0ba3a524346850a= 8c0e3bf Author: Eric Dumazet AuthorDate: Mon, 24 Aug 2026 15:51:29=20 Committer: Peter Zijlstra CommitterDate: Wed, 02 Sep 2026 09:18:03 +02:00 locking/lockdep: Invalidate stale class_cache entries for zapped classes syzbot reported a lockdep splat hitting DEBUG_LOCKS_WARN_ON(1) in hlock_class() due to an invalid class_idx: WARNING: kernel/locking/lockdep.c:238 at __lock_acquire+0x382/0x2cf0 kern= el/locking/lockdep.c:5203 Workqueue: wg-crypt-wg0 wg_packet_tx_worker RIP: 0010:hlock_class kernel/locking/lockdep.c:238 [inline] RIP: 0010:check_wait_context kernel/locking/lockdep.c:4870 [inline] RIP: 0010:__lock_acquire+0x389/0x2cf0 kernel/locking/lockdep.c:5203 Call Trace: lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5886 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:173 tcp_tsq_handler+0x29/0x200 net/ipv4/tcp_output.c:1291 tcp_tsq_workfn+0x384/0x410 net/ipv4/tcp_output.c:1325 ... When a lock class is zapped (e.g. during module unload or key unregistration), zap_class() clears the class's bit in lock_classes_in_use and removes it from the class hash table. However, existing lockdep_map instances embedded in data structures may still retain a pointer to the zapped class in their class_cache[] array. When __lock_acquire() subsequently runs on such a lock, it finds lock->class_cache[subclass] !=3D NULL, skipping register_lock_class() and assigning hlock->class_idx to the index of the zapped class. When check_wait_context() or hlock_class() inspects the held_lock, it finds !test_bit(class_idx, lock_classes_in_use) and warns. Furthermore, if the zapped slot is subsequently re-allocated to an unrelated lock key, the stale class_cache entry would erroneously match the unrelated class (ABA issue). Add lock_class_cache_is_valid() to validate that the cached class is within lock_classes bounds, still allocated in lock_classes_in_use (using uninstrumented arch_test_bit() in __always_inline context so it is safe in noinstr contexts like match_held_lock()), and that class->key matches the expected subkey (taking lockdep_set_subclass() overrides into account). Also use READ_ONCE()/WRITE_ONCE() when accessing class_cache[]. If the entry is invalid or stale, fall back to register_lock_class() / look_up_lock_class(). Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer= in use") Closes: https://lore.kernel.org/netdev/6a8c66dc.4d75e56a.c9a88.0050.GAE@goo= gle.com/T/#u Reported-by: syzbot+2d770620059281e225a4@syzkaller.appspotmail.com Assisted-by: Gemini:gemini-3.1-pro Signed-off-by: Eric Dumazet Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260824155129.676096-1-edumazet@google.com --- kernel/locking/lockdep.c | 50 ++++++++++++++++++++++++++++++++------- 1 file changed, 42 insertions(+), 8 deletions(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 25d77d4..763f798 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -963,6 +963,34 @@ look_up_lock_class(const struct lockdep_map *lock, uns= igned int subclass) return NULL; } =20 +static __always_inline bool lock_class_cache_is_valid(const struct lockdep= _map *lock, + const struct lock_class *class, + unsigned int subclass) +{ + unsigned int class_subclass; + + if (!class) + return false; + + if (unlikely(class < lock_classes || class >=3D lock_classes + MAX_LOCKDE= P_KEYS)) + return false; + + if (unlikely(!arch_test_bit(class - lock_classes, lock_classes_in_use))) + return false; + + if (unlikely(!lock->key)) + return false; + + class_subclass =3D subclass ? subclass : class->subclass; + if (unlikely(class_subclass >=3D MAX_LOCKDEP_SUBCLASSES)) + return false; + + if (unlikely(READ_ONCE(class->key) !=3D lock->key->subkeys + class_subcla= ss)) + return false; + + return true; +} + /* * Static locks do not have their class-keys yet - for them the key is * the lock object itself. If the lock is in the per cpu area, the @@ -1395,9 +1423,9 @@ out_unlock_set: =20 out_set_class_cache: if (!subclass || force) - lock->class_cache[0] =3D class; + WRITE_ONCE(lock->class_cache[0], class); else if (subclass < NR_LOCKDEP_CACHING_CLASSES) - lock->class_cache[subclass] =3D class; + WRITE_ONCE(lock->class_cache[subclass], class); =20 /* * Hash collision, did we smoke some? We found a class with a matching @@ -4957,7 +4985,7 @@ void lockdep_init_map_type(struct lockdep_map *lock, = const char *name, int i; =20 for (i =3D 0; i < NR_LOCKDEP_CACHING_CLASSES; i++) - lock->class_cache[i] =3D NULL; + WRITE_ONCE(lock->class_cache[i], NULL); =20 #ifdef CONFIG_LOCK_STAT lock->cpu =3D raw_smp_processor_id(); @@ -5022,12 +5050,15 @@ EXPORT_SYMBOL_GPL(__lockdep_no_track__); void lockdep_set_lock_cmp_fn(struct lockdep_map *lock, lock_cmp_fn cmp_fn, lock_print_fn print_fn) { - struct lock_class *class =3D lock->class_cache[0]; + struct lock_class *class =3D READ_ONCE(lock->class_cache[0]); unsigned long flags; =20 raw_local_irq_save(flags); lockdep_recursion_inc(); =20 + if (!lock_class_cache_is_valid(lock, class, 0)) + class =3D NULL; + if (!class) class =3D register_lock_class(lock, 0, 0); =20 @@ -5119,8 +5150,11 @@ static int __lock_acquire(struct lockdep_map *lock, = unsigned int subclass, if (DEBUG_LOCKS_WARN_ON(subclass >=3D MAX_LOCKDEP_SUBCLASSES)) return 0; =20 - if (subclass < NR_LOCKDEP_CACHING_CLASSES) - class =3D lock->class_cache[subclass]; + if (subclass < NR_LOCKDEP_CACHING_CLASSES) { + class =3D READ_ONCE(lock->class_cache[subclass]); + if (!lock_class_cache_is_valid(lock, class, subclass)) + class =3D NULL; + } /* * Not cached? */ @@ -5323,9 +5357,9 @@ static noinstr int match_held_lock(const struct held_= lock *hlock, return 1; =20 if (hlock->references) { - const struct lock_class *class =3D lock->class_cache[0]; + const struct lock_class *class =3D READ_ONCE(lock->class_cache[0]); =20 - if (!class) + if (!lock_class_cache_is_valid(lock, class, 0)) class =3D look_up_lock_class(lock, 0); =20 /*