From nobody Wed Dec 17 10:19:51 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AAF2014F70; Sat, 19 Jul 2025 17:40:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752946820; cv=none; b=Qkg+NNku/YbPNonEnpLU08DoY9raILZb1HDetE6rtVuRfhmEb0WqC2Va6B4zYq1lzQ5/xa/Wt6s+W7mpCkjNNGZbAv59PBAOWSOX1z8VxkJbrdUIBy5XYqbLssEurNt8arzQttFKJSg58+FtdvSJNxOjmc2Xi7JPeAcuRYt0FUQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752946820; c=relaxed/simple; bh=skA+4fBR0hDXfHQbYxzqz2vHn2KoxBleGr+cwaLJA5Q=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=mPzh1ozB3A7eFnz0Qly7iP/G6hhufNcsDKM+zsEE9rG8lhEXiuY9uxA9vIEG29O0j5u2bx+w50nDEslK5SaFwk2P7KoxVN2AfKu6CtmdMawuiUOYOcHgl01BsEcB+/Rqh5EQf++o5dd3rKwpc9NtizYMdeFYz68zcY26srnEpmE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=VTRylTqn; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=NYqQuvQA; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="VTRylTqn"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="NYqQuvQA" Date: Sat, 19 Jul 2025 17:40:07 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1752946810; 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=r632AJmrCiQlyKzNh7POBFi39iChlZhD+Q0eTj98DK4=; b=VTRylTqnqNO1dpOIo1cHKNQcQLIia2yruPccg9WcGtlCqxZaj2Me8/ViiTdLpJ9TynO1Ur 1p50zhPA5YrUpXHmjGNwGX4tWLfw+aYxlw2lyWsUtThZX40NcpeCeX5Aw/LkmS31UMc4DS G7yqIhkwG8dguLErpCMRg2/j71n5x8FT2Fo1WFp4/0EmVHAE+li+V4i1fTODOKPNYregP6 wD1XrpgJMvn2EyPLT9WiI8ypt7byLXPfcm7Oki/3kvh+xPlhvZswnp4WUt0N+DU0MBq2u7 T8sOHyTW7+kS46DxWDQ/6VFHpZgTxRM4PCQ0Nhz3n8TC8oyswrdDCYCto56ynA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1752946810; 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=r632AJmrCiQlyKzNh7POBFi39iChlZhD+Q0eTj98DK4=; b=NYqQuvQA1D07u3LdpgaFFwImYm9LjLsu/+etNw0HAGAV4x/gqSygGkmN/Pp3tuxzr+1/TK uSbJq0YgWMbhUyAA== From: "tip-bot2 for Breno Leitao" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/core] lockdep: Speed up lockdep_unregister_key() with expedited RCU synchronization Cc: Erik Lundgren , Breno Leitao , "Paul E. McKenney" , Eric Dumazet , Boqun Feng , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20250321-lockdep-v1-1-78b732d195fb@debian.org> References: <20250321-lockdep-v1-1-78b732d195fb@debian.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <175294680733.1420.1210512165865622668.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/core branch of tip: Commit-ID: 7a3cedafccf8e7d038ad4cfec5b38052647ceac5 Gitweb: https://git.kernel.org/tip/7a3cedafccf8e7d038ad4cfec5b380526= 47ceac5 Author: Breno Leitao AuthorDate: Fri, 21 Mar 2025 02:30:49 -07:00 Committer: Boqun Feng CommitterDate: Mon, 14 Jul 2025 21:57:29 -07:00 lockdep: Speed up lockdep_unregister_key() with expedited RCU synchronizati= on 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 [boqun: Fixed the comment and add more information for the temporary workaround, and add TODO information for hazptr] Reported-by: Erik Lundgren Signed-off-by: Breno Leitao Reviewed-by: Paul E. McKenney Reviewed-by: Eric Dumazet Signed-off-by: Boqun Feng Link: https://lore.kernel.org/r/20250321-lockdep-v1-1-78b732d195fb@debian.o= rg --- kernel/locking/lockdep.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 0c94141..2d4c5ba 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -6616,8 +6616,16 @@ 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. + * + * Some operations like __qdisc_destroy() will call this in a debug + * kernel, and the network traffic is disabled while waiting, hence + * the delay of the wait matters in debugging cases. Currently use a + * synchronize_rcu_expedited() to speed up the wait at the cost of + * system IPIs. TODO: Replace RCU with hazptr for this. + */ + synchronize_rcu_expedited(); } EXPORT_SYMBOL_GPL(lockdep_unregister_key); =20