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[2620:137:e000::1:20]) by mx.google.com with ESMTP id n7-20020a170902f60700b0016d7639681dsi336269plg.493.2022.10.24.12.31.09; Mon, 24 Oct 2022 12:31:23 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=VOS48z8P; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231171AbiJXTam (ORCPT + 99 others); Mon, 24 Oct 2022 15:30:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59450 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233222AbiJXT2v (ORCPT ); Mon, 24 Oct 2022 15:28:51 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B91D6B5FF0 for ; Mon, 24 Oct 2022 11:00:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1666634341; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+XFNqhe/9TyVt9WobmDUsN79a+94gmZaId1xsUvIpII=; b=VOS48z8PIvfgSnGvEuhWrINbbG60figtq7oLWt95Vy6onN9oZeNAOMTts5GuyoNXJ2OHm/ A+yaq1XtK8hZmUW1pgPl5Vf8a5IU6nyRPl8+/Jqe6yEmcw5D8IKup4ZKceqmLWvIoJ/0V0 HQiPPcYmCsLYUPa8o4KJ9IIFx9Ra32M= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-104-k9qH5hQlNIiEGiRqsutV4A-1; Mon, 24 Oct 2022 13:44:52 -0400 X-MC-Unique: k9qH5hQlNIiEGiRqsutV4A-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 37353803D4B; Mon, 24 Oct 2022 17:44:51 +0000 (UTC) Received: from llong.com (dhcp-17-153.bos.redhat.com [10.18.17.153]) by smtp.corp.redhat.com (Postfix) with ESMTP id E6073492B0F; Mon, 24 Oct 2022 17:44:50 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng Cc: linux-kernel@vger.kernel.org, john.p.donnelly@oracle.com, Hillf Danton , Mukesh Ojha , =?utf-8?b?VGluZzExIFdhbmcg546L5am3?= , Waiman Long Subject: [PATCH v4 3/5] locking/rwsem: Change waiter->hanodff_set to a handoff_state enum Date: Mon, 24 Oct 2022 13:44:16 -0400 Message-Id: <20221024174418.796468-4-longman@redhat.com> In-Reply-To: <20221024174418.796468-1-longman@redhat.com> References: <20221024174418.796468-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE 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-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1747598582523556636?= X-GMAIL-MSGID: =?utf-8?q?1747598582523556636?= Change the boolean waiter->handoff_set to an enum type so that we can have more states in some later patches. Also use READ_ONCE() outside wait_lock critical sections for read and WRITE_ONCE() inside wait_lock critical sections for write for proper synchronization. There is no functional change. Signed-off-by: Waiman Long --- kernel/locking/rwsem.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index c68d76fc8c68..a8bfc905637a 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -338,12 +338,17 @@ enum rwsem_waiter_type { RWSEM_WAITING_FOR_READ }; +enum rwsem_handoff_state { + HANDOFF_NONE = 0, + HANDOFF_REQUESTED, +}; + struct rwsem_waiter { struct list_head list; struct task_struct *task; enum rwsem_waiter_type type; + enum rwsem_handoff_state handoff_state; unsigned long timeout; - bool handoff_set; }; #define rwsem_first_waiter(sem) \ list_first_entry(&sem->wait_list, struct rwsem_waiter, list) @@ -470,7 +475,7 @@ static void rwsem_mark_wake(struct rw_semaphore *sem, adjustment -= RWSEM_FLAG_HANDOFF; lockevent_inc(rwsem_rlock_handoff); } - waiter->handoff_set = true; + WRITE_ONCE(waiter->handoff_state, HANDOFF_REQUESTED); } atomic_long_add(-adjustment, &sem->count); @@ -622,7 +627,7 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, * waiter is the one that set it. Otherwisee, we * still try to acquire the rwsem. */ - if (first->handoff_set && (waiter != first)) + if (first->handoff_state && (waiter != first)) return false; } @@ -650,11 +655,11 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, /* * We have either acquired the lock with handoff bit cleared or set - * the handoff bit. Only the first waiter can have its handoff_set + * the handoff bit. Only the first waiter can have its handoff_state * set here to enable optimistic spinning in slowpath loop. */ if (new & RWSEM_FLAG_HANDOFF) { - first->handoff_set = true; + WRITE_ONCE(first->handoff_state, HANDOFF_REQUESTED); lockevent_inc(rwsem_wlock_handoff); return false; } @@ -1043,7 +1048,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat waiter.task = current; waiter.type = RWSEM_WAITING_FOR_READ; waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT; - waiter.handoff_set = false; + waiter.handoff_state = HANDOFF_NONE; raw_spin_lock_irq(&sem->wait_lock); if (list_empty(&sem->wait_list)) { @@ -1131,7 +1136,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) waiter.task = current; waiter.type = RWSEM_WAITING_FOR_WRITE; waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT; - waiter.handoff_set = false; + waiter.handoff_state = HANDOFF_NONE; raw_spin_lock_irq(&sem->wait_lock); rwsem_add_waiter(sem, &waiter); @@ -1176,7 +1181,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) * In this case, we attempt to acquire the lock again * without sleeping. */ - if (waiter.handoff_set) { + if (READ_ONCE(waiter.handoff_state)) { enum owner_state owner_state; preempt_disable();