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 X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 190D7C76195 for ; Thu, 18 Jul 2019 13:53:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3D2F2173E for ; Thu, 18 Jul 2019 13:53:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="q6Spbf+g" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390650AbfGRNxo (ORCPT ); Thu, 18 Jul 2019 09:53:44 -0400 Received: from merlin.infradead.org ([205.233.59.134]:43920 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390574AbfGRNxh (ORCPT ); Thu, 18 Jul 2019 09:53:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-Id:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=q0KGUBYy1+/7QlMG960RGlggnhNzObvuQQ3z5su4p10=; b=q6Spbf+gLD099kzuQ1i67Mg0x0 o9Bds4PAfrdwAqPevfxygjFJUPB+9Ey0E3eUs3/MWjh5/MBgE9M0wgMmqhaN1Al8yfokaImPFQ922 M5uK4eRkmwkTahjeULcKC5c1SWZrBXC7x3cjClp1R2YIS6OEITNEJbzok2RYZIbej6sK4EJ13t5w8 +AJyc6FeGRy4RCYjJQz/OQImWWRv9pif5+N5o3ASEISx1tTY26PN4yLMDR2Uhe7hhMT+YBorlJ3TK u3UB6xqpTKNMGV8X9RDLrmQZ+7vZXtAC4TzetAIu9zCx/h/sVAEDp+NnmTyJqfVcY49B8zw2xjqxz fU5bsnoA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1ho6qb-0003u6-Fk; Thu, 18 Jul 2019 13:53:25 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id D4DBD20B979A6; Thu, 18 Jul 2019 15:53:22 +0200 (CEST) Message-Id: <20190718135206.228078863@infradead.org> User-Agent: quilt/0.65 Date: Thu, 18 Jul 2019 15:49:58 +0200 From: Peter Zijlstra To: Will Deacon Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Jan Stancek , Waiman Long , dbueso@suse.de, mingo@redhat.com, jade.alglave@arm.com, paulmck@linux.vnet.ibm.com Subject: [PATCH 4/4] rwsem: Add ACQUIRE comments References: <20190718134954.496297975@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since we just reviewed read_slowpath for ACQUIRE correctness, add a few coments to retain our findings. Acked-by: Will Deacon Signed-off-by: Peter Zijlstra (Intel) --- kernel/locking/rwsem.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -1000,6 +1000,7 @@ rwsem_down_read_slowpath(struct rw_semap atomic_long_add(-RWSEM_READER_BIAS, &sem->count); adjustment = 0; if (rwsem_optimistic_spin(sem, false)) { + /* rwsem_optimistic_spin() implies ACQUIRE on success */ /* * Wake up other readers in the wait list if the front * waiter is a reader. @@ -1014,6 +1015,7 @@ rwsem_down_read_slowpath(struct rw_semap } return sem; } else if (rwsem_reader_phase_trylock(sem, waiter.last_rowner)) { + /* rwsem_reader_phase_trylock() implies ACQUIRE on success */ return sem; } @@ -1067,10 +1069,10 @@ rwsem_down_read_slowpath(struct rw_semap wake_up_q(&wake_q); /* wait to be given the lock */ - while (true) { + for (;;) { set_current_state(state); if (!smp_load_acquire(&waiter.task)) { - /* Orders against rwsem_mark_wake()'s smp_store_release() */ + /* Matches rwsem_mark_wake()'s smp_store_release(). */ break; } if (signal_pending_state(state, current)) { @@ -1078,6 +1080,7 @@ rwsem_down_read_slowpath(struct rw_semap if (waiter.task) goto out_nolock; raw_spin_unlock_irq(&sem->wait_lock); + /* Ordered by sem->wait_lock against rwsem_mark_wake(). */ break; } schedule(); @@ -1087,6 +1090,7 @@ rwsem_down_read_slowpath(struct rw_semap __set_current_state(TASK_RUNNING); lockevent_inc(rwsem_rlock); return sem; + out_nolock: list_del(&waiter.list); if (list_empty(&sem->wait_list)) { @@ -1127,8 +1131,10 @@ rwsem_down_write_slowpath(struct rw_sema /* do optimistic spinning and steal lock if possible */ if (rwsem_can_spin_on_owner(sem, RWSEM_WR_NONSPINNABLE) && - rwsem_optimistic_spin(sem, true)) + rwsem_optimistic_spin(sem, true)) { + /* rwsem_optimistic_spin() implies ACQUIRE on success */ return sem; + } /* * Disable reader optimistic spinning for this rwsem after @@ -1188,9 +1194,11 @@ rwsem_down_write_slowpath(struct rw_sema wait: /* wait until we successfully acquire the lock */ set_current_state(state); - while (true) { - if (rwsem_try_write_lock(sem, wstate)) + for (;;) { + if (rwsem_try_write_lock(sem, wstate)) { + /* rwsem_try_write_lock() implies ACQUIRE on success */ break; + } raw_spin_unlock_irq(&sem->wait_lock);