From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6EAFBC4332F for ; Tue, 18 Oct 2022 00:09:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229660AbiJRAJB (ORCPT ); Mon, 17 Oct 2022 20:09:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36370 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231367AbiJRAIT (ORCPT ); Mon, 17 Oct 2022 20:08:19 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1321F86889; Mon, 17 Oct 2022 17:07:58 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6ECEBB81BE3; Tue, 18 Oct 2022 00:07:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4168BC433D6; Tue, 18 Oct 2022 00:07:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666051675; bh=SgkjwT6v/aZrh3kwyQxdb4EprkFZCGb0ZaVoc8w3ZXc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kLl20I5sHy+uwXgbVuv7GhuflgH5Rp/HW8IvQawfWqUcilowAt5/iAfuxHsglfo78 h8TxvW5xGA3/IIjiYR/ln9zcQuRm8iFf1hA1tP17QEnyja3Z36qJgaWVtl9OVFllcj 04jEZjDxpSVc439GCBJ2rgk69AhG8zEb6NSHfXRwGf4grqacZG+H8+uycNssDj+l/3 yR4WjzEem72PmngKeGgWZlvpf90rAm7f2aV9IJAQKuqpzz3tK9YpvWS9A08IFcN5+P bip2DCu+lIsTcIhVT/vWRkslXkuTBLIl9eoHJNbGqc/iNlkTgPWmVDo/lOPs1QOLtV +27PNqh2mBRrA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Gokul krishna Krishnakumar , Mukesh Ojha , Peter Zijlstra , Waiman Long , Sasha Levin , mingo@redhat.com, will@kernel.org Subject: [PATCH AUTOSEL 6.0 11/32] locking/rwsem: Disable preemption while trying for rwsem lock Date: Mon, 17 Oct 2022 20:07:08 -0400 Message-Id: <20221018000729.2730519-11-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20221018000729.2730519-1-sashal@kernel.org> References: <20221018000729.2730519-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Gokul krishna Krishnakumar [ Upstream commit 48dfb5d2560d36fb16c7d430c229d1604ea7d185 ] Make the region inside the rwsem_write_trylock non preemptible. We observe RT task is hogging CPU when trying to acquire rwsem lock which was acquired by a kworker task but before the rwsem owner was set. Here is the scenario: 1. CFS task (affined to a particular CPU) takes rwsem lock. 2. CFS task gets preempted by a RT task before setting owner. 3. RT task (FIFO) is trying to acquire the lock, but spinning until RT throttling happens for the lock as the lock was taken by CFS task. This patch attempts to fix the above issue by disabling preemption until owner is set for the lock. While at it also fix the issues at the places where rwsem_{set,clear}_owner() are called. This also adds lockdep annotation of preemption disable in rwsem_{set,clear}_owner() on Peter Z. suggestion. Signed-off-by: Gokul krishna Krishnakumar Signed-off-by: Mukesh Ojha Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Waiman Long Link: https://lore.kernel.org/r/1662661467-24203-1-git-send-email-quic_mojha@quicinc.com Signed-off-by: Sasha Levin --- kernel/locking/rwsem.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 65f0262f635e..44873594de03 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -133,14 +133,19 @@ * the owner value concurrently without lock. Read from owner, however, * may not need READ_ONCE() as long as the pointer value is only used * for comparison and isn't being dereferenced. + * + * Both rwsem_{set,clear}_owner() functions should be in the same + * preempt disable section as the atomic op that changes sem->count. */ static inline void rwsem_set_owner(struct rw_semaphore *sem) { + lockdep_assert_preemption_disabled(); atomic_long_set(&sem->owner, (long)current); } static inline void rwsem_clear_owner(struct rw_semaphore *sem) { + lockdep_assert_preemption_disabled(); atomic_long_set(&sem->owner, 0); } @@ -251,13 +256,16 @@ static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp) static inline bool rwsem_write_trylock(struct rw_semaphore *sem) { long tmp = RWSEM_UNLOCKED_VALUE; + bool ret = false; + preempt_disable(); if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) { rwsem_set_owner(sem); - return true; + ret = true; } - return false; + preempt_enable(); + return ret; } /* @@ -1352,8 +1360,10 @@ static inline void __up_write(struct rw_semaphore *sem) DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem); + preempt_disable(); rwsem_clear_owner(sem); tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count); + preempt_enable(); if (unlikely(tmp & RWSEM_FLAG_WAITERS)) rwsem_wake(sem); } -- 2.35.1