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[2620:137:e000::3:7]) by mx.google.com with ESMTPS id k8-20020a056a00134800b00690c1a57210si18363470pfu.115.2023.09.27.20.58.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Sep 2023 20:58:31 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7; Authentication-Results: mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b="gA8E7/z/"; dkim=neutral (no key) header.i=@linutronix.de; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: from out1.vger.email (depot.vger.email [IPv6:2620:137:e000::3:0]) by snail.vger.email (Postfix) with ESMTP id 438A9821A175; Wed, 27 Sep 2023 09:03:29 -0700 (PDT) X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.103.10 at snail.vger.email Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232186AbjI0QD0 (ORCPT + 19 others); Wed, 27 Sep 2023 12:03:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55466 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232838AbjI0QDM (ORCPT ); Wed, 27 Sep 2023 12:03:12 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 70B7C121; Wed, 27 Sep 2023 09:02:35 -0700 (PDT) Date: Wed, 27 Sep 2023 18:02:31 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1695830553; h=from:from: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; bh=EdCiO/WzKECbYs7KtcCYhKCOSLS8gRQvCAW/vFRb9F4=; b=gA8E7/z/ye+UWQvTptCUxfM7HS3iYd/tK9vXkmkbp6ehYQxjZfhSnwUbo4yeTQVXJ9IyaK 8wwAtn2uo82b34MM6QBT6xBYWLHHZHhUQxGiLRWHByNXFKXmbA2NGgWBwPixIIC7qn67Q0 rXHrEqx5L933ymrrywoXolbIUbAnG0yGsz7c0XyJmjfTWkMe8gKDoTyWp+Q9+TsYh6mrfE ZNxJCnQvTyxZ13dpeZ7/wj6oYmTKRHzkxrouy8xoZEUrQ6rMcvQcIQGGMWXBr8+Rz1ibrB q0E2C/9dyj2TETBAiMJrYc13NWVAl8mzXrUff1NU3ponoQLgs3BldvxYTFfGrg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1695830553; h=from:from: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; bh=EdCiO/WzKECbYs7KtcCYhKCOSLS8gRQvCAW/vFRb9F4=; b=YReDyt9JG3c9HFVm3jjR59KBPrudAz6g1lOu804uGt8ruhv64qozjuWhLyNqZHyepfHAYV cCC1Rw8pXSmPDmAg== From: Sebastian Andrzej Siewior To: linux-kernel@vger.kernel.org, rcu@vger.kernel.org Cc: "Paul E. McKenney" , Boqun Feng , Frederic Weisbecker , Ingo Molnar , Joel Fernandes , John Ogness , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , Neeraj Upadhyay , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Waiman Long , Will Deacon , Zqiang Subject: [RFC PATCH] srcu: Use try-lock lockdep annotation for NMI-safe access. Message-ID: <20230927160231.XRCDDSK4@linutronix.de> MIME-Version: 1.0 Content-Disposition: inline X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (snail.vger.email [0.0.0.0]); Wed, 27 Sep 2023 09:03:29 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1778252263811338185 X-GMAIL-MSGID: 1778252263811338185 It is claimed that srcu_read_lock_nmisafe() NMI-safe. However it triggers a lockdep if used from NMI because lockdep expects a deadlock since nothing disables NMIs while the lock is acquired. Use a try-lock annotation for srcu_read_lock_nmisafe() to avoid lockdep complains if used from NMI. Signed-off-by: Sebastian Andrzej Siewior --- The splat: | ================================ | WARNING: inconsistent lock state | 6.6.0-rc3-rt5+ #85 Not tainted | -------------------------------- | inconsistent {INITIAL USE} -> {IN-NMI} usage. | swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes: | ffffffff828e6c90 (console_srcu){....}-{0:0}, at: console_srcu_read_lock+0x3a/0x50 | {INITIAL USE} state was registered at: … | CPU0 | ---- | lock(console_srcu); | | lock(console_srcu); | | *** DEADLOCK *** | My guess is that trylock annotation should not apply to rcu_lock_acquire(). This would distinguish it from from non-NMI safe srcu_read_lock_nmisafe() and NMI check in rcu_read_unlock() is only there to survive if accidentally used in-NMI. include/linux/rcupdate.h | 6 ++++++ include/linux/srcu.h | 2 +- 2 files changed, 7 insertions(+), 1 deletion(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 5e5f920ade909..44aab5c0bd2c1 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -303,6 +303,11 @@ static inline void rcu_lock_acquire(struct lockdep_map *map) lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); } +static inline void rcu_try_lock_acquire(struct lockdep_map *map) +{ + lock_acquire(map, 0, 1, 2, 0, NULL, _THIS_IP_); +} + static inline void rcu_lock_release(struct lockdep_map *map) { lock_release(map, _THIS_IP_); @@ -317,6 +322,7 @@ int rcu_read_lock_any_held(void); #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ # define rcu_lock_acquire(a) do { } while (0) +# define rcu_try_lock_acquire(a) do { } while (0) # define rcu_lock_release(a) do { } while (0) static inline int rcu_read_lock_held(void) diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 127ef3b2e6073..236610e4a8fa5 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -229,7 +229,7 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp srcu_check_nmi_safety(ssp, true); retval = __srcu_read_lock_nmisafe(ssp); - rcu_lock_acquire(&ssp->dep_map); + rcu_try_lock_acquire(&ssp->dep_map); return retval; }