From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qv1-f72.google.com (mail-qv1-f72.google.com [209.85.219.72]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BD16644CF29 for ; Mon, 24 Aug 2026 15:51:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.72 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787586694; cv=none; b=civvnZwwj0mXHV9wM0HLBKaBih8H374hldVld1nMzKsV719vvo6CBJMk6Km52KOgTAt1SOIW+6Y9bJ9NT+cuNFs66nB4/UralBsi0ElkJhup4G3lgTb9cn8fnoxv7DAuPm6KlDwzvUHFYJWILEreivY/1WWuWO633aky7V6aBBI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787586694; c=relaxed/simple; bh=zXB98oGFU5Gil7Rk9HFojNt2ZTBLvE1zLymx6VtnklY=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=bY17Rx0S13LWIw0OGNlURElzV906BAUN1WTu4wncO8vElNMOfD1f4r4wT2O70xU2HFk+43T7MU5wLsG6RyhhLAlV0cQ8hiM60LfQNLbSV2Vi4jKPqZEok52CYddQiIk5LQqBcSQDXnTjuVDX50YfBOvWUfCaQ5OIaM5U0CulVTg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--edumazet.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=v9OT4rnD; arc=none smtp.client-ip=209.85.219.72 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--edumazet.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="v9OT4rnD" Received: by mail-qv1-f72.google.com with SMTP id 6a1803df08f44-90c8cb9f37eso26072706d6.0 for ; Mon, 24 Aug 2026 08:51:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1787586692; x=1788191492; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:mime-version:date:from :to:cc:subject:date:message-id:reply-to:content-type; bh=AEBz1cefQGrzLTsdFlMZLzUk+Ij8Jfd1qZk6z9JQqNQ=; b=v9OT4rnD1VHD2nPrErL9sGlL7SH8L0HVGM91mW/oNhYgqPG5Qv3KTkCL/MWeQsS+qD Ot6XLCwD6zSEjIk8Nr36Rxs03x0GPE8EgiuKJVkJjC2UoUU/ht0nKbtubXI98C4FXZXw AbLP3UtCDFKPAnovW4/BbnT+9Hp8GZ6GUZGcNaInwchWXPS4e4v1+JwgMT50y3Li4NF5 2FG2vWBX/uWVIjDpCppuKQArilfva1MGYlSn4jwetZVmmBU+9jteyaK/HeaAq1PHXc0p koceCPCckg8bWSHBCX5ndffpwyUiS6Xy3ELufaZH+I5KywtuvA/SIKR+O0kQckz7rL37 1+wQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787586692; x=1788191492; h=content-type:cc:to:from:subject:message-id:mime-version:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=AEBz1cefQGrzLTsdFlMZLzUk+Ij8Jfd1qZk6z9JQqNQ=; b=kAdkMg/sK4R15AKVdD9OtxPxWYDmid3XKRoONggWMjLGdNWO8glGNtKfDsvx9FfSpQ /BBLu/iMKmZxvsQMR08Fci0w6E3ze4IjbzSHvoXQz10O1R5ZMndaJrGWZtJGOMoH7QAe KFt4l1NjDhBHdyqFaLASRTD8FphbSvySpVR7i898HxM5wXo2FIcfano1/yh6fuB6O2iB vGQEISvydEQ+08Bo/ROnvtsXuTA7zVUKuFDNiUL8DemHLExtEpi0e+/5luhXzOYRwwKS 7IIU5nGeVtKpRNdx+OGt0oHe1tXzaRE3aSsxJrm8kG4cRFD3BzMCCpzQG8ksthtHe4NS Lexw== X-Gm-Message-State: AFuF++kwJdfR6ugEcX+qKDv6TtA+HscV5kg0yOkdUrqXVh3OEsKR1Jdz Op/m+ontCPCKV7lwtsD5KECVuYVzs1rADbO8cU3yFfvBysztxZ+FanOP74civ8JPlOFoWLe6RfK K936K5D745XruzQ== X-Received: from qvbpn9.prod.google.com ([2002:a05:6214:1309:b0:907:52b7:d39b]) (user=edumazet job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6214:508d:b0:8f2:747d:3027 with SMTP id 6a1803df08f44-90c80fbb548mr256612556d6.20.1787586691226; Mon, 24 Aug 2026 08:51:31 -0700 (PDT) Date: Mon, 24 Aug 2026 15:51:29 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.55.0.766.g2966f0265a-goog Message-ID: <20260824155129.676096-1-edumazet@google.com> Subject: [PATCH] locking/lockdep: Invalidate stale class_cache entries for zapped classes From: Eric Dumazet To: Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , Waiman Long Cc: linux-kernel , netdev@vger.kernel.org, Eric Dumazet , syzbot+2d770620059281e225a4@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" 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 kernel/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] != 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") Reported-by: syzbot+2d770620059281e225a4@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6a8c66dc.4d75e56a.c9a88.0050.GAE@google.com/T/#u Assisted-by: Gemini:gemini-3.1-pro Signed-off-by: Eric Dumazet --- 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 25d77d4a1061..763f79806bd8 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -963,6 +963,34 @@ look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass) return NULL; } +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 >= lock_classes + MAX_LOCKDEP_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 = subclass ? subclass : class->subclass; + if (unlikely(class_subclass >= MAX_LOCKDEP_SUBCLASSES)) + return false; + + if (unlikely(READ_ONCE(class->key) != lock->key->subkeys + class_subclass)) + 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 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) out_set_class_cache: if (!subclass || force) - lock->class_cache[0] = class; + WRITE_ONCE(lock->class_cache[0], class); else if (subclass < NR_LOCKDEP_CACHING_CLASSES) - lock->class_cache[subclass] = class; + WRITE_ONCE(lock->class_cache[subclass], class); /* * 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; for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++) - lock->class_cache[i] = NULL; + WRITE_ONCE(lock->class_cache[i], NULL); #ifdef CONFIG_LOCK_STAT lock->cpu = 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 = lock->class_cache[0]; + struct lock_class *class = READ_ONCE(lock->class_cache[0]); unsigned long flags; raw_local_irq_save(flags); lockdep_recursion_inc(); + if (!lock_class_cache_is_valid(lock, class, 0)) + class = NULL; + if (!class) class = register_lock_class(lock, 0, 0); @@ -5119,8 +5150,11 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, if (DEBUG_LOCKS_WARN_ON(subclass >= MAX_LOCKDEP_SUBCLASSES)) return 0; - if (subclass < NR_LOCKDEP_CACHING_CLASSES) - class = lock->class_cache[subclass]; + if (subclass < NR_LOCKDEP_CACHING_CLASSES) { + class = READ_ONCE(lock->class_cache[subclass]); + if (!lock_class_cache_is_valid(lock, class, subclass)) + class = NULL; + } /* * Not cached? */ @@ -5323,9 +5357,9 @@ static noinstr int match_held_lock(const struct held_lock *hlock, return 1; if (hlock->references) { - const struct lock_class *class = lock->class_cache[0]; + const struct lock_class *class = READ_ONCE(lock->class_cache[0]); - if (!class) + if (!lock_class_cache_is_valid(lock, class, 0)) class = look_up_lock_class(lock, 0); /* base-commit: 0a0d1d55dad570724bf8c7ea83409639cfb4be9b -- 2.55.0.766.g2966f0265a-goog