From nobody Wed Dec 17 10:22:56 2025 Received: from mail-ej1-f43.google.com (mail-ej1-f43.google.com [209.85.218.43]) (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 D07A71E5707; Fri, 21 Mar 2025 09:31:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.43 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742549472; cv=none; b=KBSo9UN9UWgCpYNB1aQykVyJepJ4Gp/5seSfYOrRg7qv0UQH/o9DRUh6mviXK+RDTC67fXHGTk+WqysLJ/cKS5FJ9bKg41nNFpE7d7ZKAa5a/SwA3eQV5Gg42LmX2pCm66FzSnQin+9ZYIHlCYCbdrCvlRZw8LBy0DepLc/bb5s= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742549472; c=relaxed/simple; bh=Y6I/8vVmdfk6sGCvQTPk4i11HKqhHcWpJd91MnYDdOk=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=TXHGY79XJCnR8mot8lCY2mkUNNwwjM/ELK/mzijUUV5jtW6SSwQjvHpPMpFVGwiQ4r3Ld8+T4CcHNd8e3PhRMBFMfNi1AxqwTjK18QLzs9ULR6v/ospfSnYcTQfYN0+0JKx8+wme0pMf02KnH8AF6YyUQaDOwrmgsqSjzp1agVg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=debian.org; spf=pass smtp.mailfrom=gmail.com; arc=none smtp.client-ip=209.85.218.43 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=debian.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-ej1-f43.google.com with SMTP id a640c23a62f3a-aaecf50578eso349084866b.2; Fri, 21 Mar 2025 02:31:10 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1742549469; x=1743154269; h=cc:to:message-id:content-transfer-encoding:mime-version:subject :date:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=W/NPUaREURJ6mCKVAccGEeQmvtTeXxq8+4zuow6YaFw=; b=rWHQlOigmqcksMmd1Gbrl0B7d/55p5uwBnHKhy9SV39PV+i5Llax5CuoeuwaHF0QhZ sZj5gzynWzZi8vjaTpP2rH5cZxgi6aPNb6Vrbo6xJo/uzRl5iTUYRktuD77L2e/AQ7IE JFyiLxrhSHrxVXNMTheREcKp0FXUYo2n7s0jeY/oKIxCqU/jHsL1XO6FDsoRmnGIJ3qE HnjyPAs6u574s5ZvxX3GEBmgnxN57GViuqUhRxHkZNVzONpcoaQj5afn5tGzvkhZ6e2J quvqrlvzE8DW3sB7nRysXVkG86jlBzdX8zE1CXSFbQabkYaDWUjoaIvQkVlFJhty3DHB EoaA== X-Forwarded-Encrypted: i=1; AJvYcCU5I3icIdbl5MheYRmxDu+l+LIWssVeC6DJwxrtmWV+vG13WQhX4fBo0iipQ6Kr/4z4Ft2nI+8+@vger.kernel.org, AJvYcCV5Nq7CybI/pRQykVZWMTedsPnzJ2onDzcDCMShtMCieedE1LbfsF9uq75OT8t8RqQogjHUrt2PEsxjCXs=@vger.kernel.org X-Gm-Message-State: AOJu0YztochO7roMXzCMpTtbJ7WDbTzczTwlZPrhJfpuaxpJQ0sJUKWn +zZnxt4Zux+vPCCUnM0g5T+TYvGGm99HoD5PAlAygR8zVtnWXF8q X-Gm-Gg: ASbGncsQs/Yo+5jtwtnpjJT3yRr3SoBb+gPC6U8uIdbZPVq5g16CTKOU51OsLKpuhsp d1dZe7G0lOlbHqfpfstMKtnxSmKg8bJklrsMGeFiMgW2Ah1eOBoC1Ek331ITHZ/hlnypF9eHIZx 8JmHDNPornsBvKYUsfSTEez1NOkXkTvpmK7VYNkS7EBffCLjR/35dB8XpwB4XJQ2LtRqHsLCh+0 oWNr5DHSocWPE/9JHcmDEfy6fMhzI5YyYH1ZS2Lpu2vfex9N5TxdZHCGANFISp95uNTWwyCtg20 Eo3QIvuzFwEh2/2rA0iELGfspHnzWrtVmrw= X-Google-Smtp-Source: AGHT+IF8f1GC7wbrCO3eXH1B7reEeFIOUHS0zx+PYz/rKNz+5eov4VmNDk0rBsgjC169SJCW/K90hw== X-Received: by 2002:a17:907:6e87:b0:ac3:2d47:f6af with SMTP id a640c23a62f3a-ac3f212b833mr201431266b.20.1742549468664; Fri, 21 Mar 2025 02:31:08 -0700 (PDT) Received: from localhost ([2a03:2880:30ff:8::]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ac3ef8676c2sm116468566b.9.2025.03.21.02.31.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Mar 2025 02:31:07 -0700 (PDT) From: Breno Leitao Date: Fri, 21 Mar 2025 02:30:49 -0700 Subject: [PATCH] lockdep: Speed up lockdep_unregister_key() with expedited RCU synchronization Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250321-lockdep-v1-1-78b732d195fb@debian.org> X-B4-Tracking: v=1; b=H4sIAMgx3WcC/x3M4QpAMBQG0Fe5fb+tNmyyV5EfMxc3QltJybsr5 wHOg8xJOMPTg8SXZDl2eDIFIS5hn1nJCE8odWl1ZVq1HXEd+VSD4Rh03bTOWRSEM/Ek9z91/ft +5JbwcFkAAAA= X-Change-ID: 20250319-lockdep-b1eca0479665 To: Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , Waiman Long Cc: aeh@meta.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, edumazet@google.com, jhs@mojatatu.com, kernel-team@meta.com, Erik Lundgren , Breno Leitao , "Paul E. McKenney" X-Mailer: b4 0.15-dev-42535 X-Developer-Signature: v=1; a=openpgp-sha256; l=2142; i=leitao@debian.org; h=from:subject:message-id; bh=Y6I/8vVmdfk6sGCvQTPk4i11HKqhHcWpJd91MnYDdOk=; b=owEBbQKS/ZANAwAIATWjk5/8eHdtAcsmYgBn3THacqvxp5klqqqxekE7OYBsb7EMCXA8usIVX OhVJnYS046JAjMEAAEIAB0WIQSshTmm6PRnAspKQ5s1o5Of/Hh3bQUCZ90x2gAKCRA1o5Of/Hh3 bWszEACxTC+Ie5buHGAr7rv5ihfTYSdVtFYTgDBg7vdatWsfs39+6AdMD/p3O4eqUWs/e/TTGRy sTIMHuNC6FbfEfqY/2J6+OGybKh0B7GIZhCnos3xAAst7oR1knZ0PsYqEWVZK7dkkWLlTCYycAQ J5FIn816Grs4G8L2hEZk/VLuSxSlCDe1XSBOfSF79ltHk7DqUgcIzc0O8y+S/kkgfDVvJFzxgfE GEHclgsI/bZv71856R5aSS1Z0tF7IpfJV7I6TShhjquYYjFnuTu/4VgBK16lG8gPfx79cIO4lMg pcj74c6Wt/UhSONLbTz267UgUhCmA6uzmaq/mIRwD/z91enQmqJG6T0lPMWrA9m3BVFgA1hDaIo vSu9xrMtCkiGRtXwLuaIPbkFRp6U5D+YVHhhRwwzAiPnevFrfs4lye5dfpQtdybiqW6VAByfpfC RLemQxsdOrixHpjQen9hWl894MFOJWq2kp+uWSRb8UdYt4rBIc/GAo5r/pFRktxtEtOH5S3d2Gc GpvMGss3Y2ELlcj4/6AndV6OwYKEUiLLupkxPC1gTc2eNjaOPokDj6gafjH7fcYtnL+AZ43Yk9G k9IvikeSZhkX1uf5QozaaHOxlRf39WYHB8CuuMJ6nmi4mxs7IYs8IxC1ZUHRGmJA9Q54mXxsCW9 dqp8+dNwrQU7qOA== X-Developer-Key: i=leitao@debian.org; a=openpgp; fpr=AC8539A6E8F46702CA4A439B35A3939FFC78776D lockdep_unregister_key() is called from critical code paths, including sections where rtnl_lock() is held. For example, when replacing a qdisc in a network device, network egress traffic is disabled while __qdisc_destroy() is called for every network queue. If lockdep is enabled, __qdisc_destroy() calls lockdep_unregister_key(), which gets blocked waiting for synchronize_rcu() to complete. For example, a simple tc command to replace a qdisc could take 13 seconds: # time /usr/sbin/tc qdisc replace dev eth0 root handle 0x1: mq real 0m13.195s user 0m0.001s sys 0m2.746s During this time, network egress is completely frozen while waiting for RCU synchronization. Use synchronize_rcu_expedited() instead to minimize the impact on critical operations like network connectivity changes. This improves 10x the function call to tc, when replacing the qdisc for a network card. # time /usr/sbin/tc qdisc replace dev eth0 root handle 0x1: mq real 0m1.789s user 0m0.000s sys 0m1.613s Reported-by: Erik Lundgren Signed-off-by: Breno Leitao Reviewed-by: "Paul E. McKenney" Reviewed-by: Eric Dumazet --- kernel/locking/lockdep.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 4470680f02269..a79030ac36dd4 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -6595,8 +6595,10 @@ void lockdep_unregister_key(struct lock_class_key *k= ey) if (need_callback) call_rcu(&delayed_free.rcu_head, free_zapped_rcu); =20 - /* Wait until is_dynamic_key() has finished accessing k->hash_entry. */ - synchronize_rcu(); + /* Wait until is_dynamic_key() has finished accessing k->hash_entry. + * This needs to be quick, since it is called in critical sections + */ + synchronize_rcu_expedited(); } EXPORT_SYMBOL_GPL(lockdep_unregister_key); =20 --- base-commit: 81e4f8d68c66da301bb881862735bd74c6241a19 change-id: 20250319-lockdep-b1eca0479665 Best regards, --=20 Breno Leitao