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=-20.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 E7C50C433EF for ; Thu, 16 Sep 2021 11:59:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CFE1361241 for ; Thu, 16 Sep 2021 11:59:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238685AbhIPMAq (ORCPT ); Thu, 16 Sep 2021 08:00:46 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:47486 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238558AbhIPMAn (ORCPT ); Thu, 16 Sep 2021 08:00:43 -0400 Date: Thu, 16 Sep 2021 11:59:18 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1631793559; 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=itYHqY3gHZkcYz6Iqxhy5QlbwoSsT+monGa4y5nc82A=; b=fjPdSVBjGWUmOIuZN0HP1Ie2mJh9GswnOGSzk0TH+gMJ3+IVb0Zl6Y+5zRZgx6Bo0fiQiL 5mySVs/lbh/KdjRjFis0SwAB6q2k2C5aq660PbbusCJZh7cgD2wFgIl9zAe6IMf5BZ7yJr DIOxiSZF55FUJ7m9Khpj4nh6fi4YPoW3eq8yFZm7UNYVaJc3HYtoRYOlPYwZcYlCdfhvDk Nx+z1DNRMUDSn7gJgjI1HEyVJWbvcW/QxdK8ez3+8kqub/MWeX9Q5iuClOuKuOXyPyxjIr 1mf/fAm2s4wNIwiVAFJc7+JMJinht46iHOc9t5n/4RfpOEzLPShBaeSrKb+QRA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1631793559; 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=itYHqY3gHZkcYz6Iqxhy5QlbwoSsT+monGa4y5nc82A=; b=0kQ2Di4aR3ZL53dyGbFCLE+9bQf2Tt4yR2FCTj1OXlzwN6r3nxPjWEHA9pKvWxxUbyoVXc xFqRdp6J4LUuBNAQ== From: "tip-bot2 for Peter Zijlstra" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/urgent] locking/rwbase: Extract __rwbase_write_trylock() Cc: "Peter Zijlstra (Intel)" , Thomas Gleixner , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: References: MIME-Version: 1.0 Message-ID: <163179355883.25758.5450895206052550685.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the locking/urgent branch of tip: Commit-ID: 616be87eac9fa2ab2dca1069712f7236e50f3bf6 Gitweb: https://git.kernel.org/tip/616be87eac9fa2ab2dca1069712f7236e50f3bf6 Author: Peter Zijlstra AuthorDate: Thu, 09 Sep 2021 12:59:18 +02:00 Committer: Peter Zijlstra CommitterDate: Wed, 15 Sep 2021 17:49:15 +02:00 locking/rwbase: Extract __rwbase_write_trylock() The code in rwbase_write_lock() is a little non-obvious vs the read+set 'trylock', extract the sequence into a helper function to clarify the code. This also provides a single site to fix fast-path ordering. Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Thomas Gleixner Link: https://lkml.kernel.org/r/YUCq3L+u44NDieEJ@hirez.programming.kicks-ass.net --- kernel/locking/rwbase_rt.c | 44 +++++++++++++++++++++---------------- 1 file changed, 26 insertions(+), 18 deletions(-) diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c index 542b017..48fbbcc 100644 --- a/kernel/locking/rwbase_rt.c +++ b/kernel/locking/rwbase_rt.c @@ -196,6 +196,19 @@ static inline void rwbase_write_downgrade(struct rwbase_rt *rwb) __rwbase_write_unlock(rwb, WRITER_BIAS - 1, flags); } +static inline bool __rwbase_write_trylock(struct rwbase_rt *rwb) +{ + /* Can do without CAS because we're serialized by wait_lock. */ + lockdep_assert_held(&rwb->rtmutex.wait_lock); + + if (!atomic_read(&rwb->readers)) { + atomic_set(&rwb->readers, WRITER_BIAS); + return 1; + } + + return 0; +} + static int __sched rwbase_write_lock(struct rwbase_rt *rwb, unsigned int state) { @@ -210,34 +223,30 @@ static int __sched rwbase_write_lock(struct rwbase_rt *rwb, atomic_sub(READER_BIAS, &rwb->readers); raw_spin_lock_irqsave(&rtm->wait_lock, flags); - /* - * set_current_state() for rw_semaphore - * current_save_and_set_rtlock_wait_state() for rwlock - */ - rwbase_set_and_save_current_state(state); + if (__rwbase_write_trylock(rwb)) + goto out_unlock; - /* Block until all readers have left the critical section. */ - for (; atomic_read(&rwb->readers);) { + rwbase_set_and_save_current_state(state); + for (;;) { /* Optimized out for rwlocks */ if (rwbase_signal_pending_state(state, current)) { rwbase_restore_current_state(); __rwbase_write_unlock(rwb, 0, flags); return -EINTR; } + + if (__rwbase_write_trylock(rwb)) + break; + raw_spin_unlock_irqrestore(&rtm->wait_lock, flags); + rwbase_schedule(); + raw_spin_lock_irqsave(&rtm->wait_lock, flags); - /* - * Schedule and wait for the readers to leave the critical - * section. The last reader leaving it wakes the waiter. - */ - if (atomic_read(&rwb->readers) != 0) - rwbase_schedule(); set_current_state(state); - raw_spin_lock_irqsave(&rtm->wait_lock, flags); } - - atomic_set(&rwb->readers, WRITER_BIAS); rwbase_restore_current_state(); + +out_unlock: raw_spin_unlock_irqrestore(&rtm->wait_lock, flags); return 0; } @@ -253,8 +262,7 @@ static inline int rwbase_write_trylock(struct rwbase_rt *rwb) atomic_sub(READER_BIAS, &rwb->readers); raw_spin_lock_irqsave(&rtm->wait_lock, flags); - if (!atomic_read(&rwb->readers)) { - atomic_set(&rwb->readers, WRITER_BIAS); + if (__rwbase_write_trylock(rwb)) { raw_spin_unlock_irqrestore(&rtm->wait_lock, flags); return 1; }