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 6EF9BC4167B for ; Tue, 28 Nov 2023 21:15:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376622AbjK1VPe (ORCPT ); Tue, 28 Nov 2023 16:15:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53634 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376620AbjK1VOf (ORCPT ); Tue, 28 Nov 2023 16:14:35 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CD25559EB for ; Tue, 28 Nov 2023 13:10:15 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 91F32C43397; Tue, 28 Nov 2023 21:10:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1701205815; bh=eVFdTyVDWL+kT6If3Mn7vSnBYnyyTRQr/GOap9CwbWM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JCVzU0cdzLXwmQEyh08OOZg7Cq/uO5AE0pZtN7767EbAerknhI9cdudXseuke1rAi 1FGy3C5LqyE4wJHgP+zquneY34W0Z1xgSuFhtqKkY4mNTdpOAshlrFEv4g61fqI+wz 7qfM1kx3/6tGRJYLZgr2qRWluP/JrDTo4rDUAC4r/DafChsm0ZHr697HxPRgrwD00y 82dO5Nt/2rQ+/83wSISdqDmLKcOzzTYPl1U9Ppco83fD+CRJ+b5tq3bDjh+TN/33Lq +vifAcqCe4bm313WDmniuqYA+6ayOrgvX69liuDuK8d7pJfUrVKZ7ximd9n/PAUafq fv5KRVZ5QrhtQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Linus Torvalds , Guo Ren , Ingo Molnar , Waiman Long , Sasha Levin , linux-arch@vger.kernel.org Subject: [PATCH AUTOSEL 4.19 09/10] asm-generic: qspinlock: fix queued_spin_value_unlocked() implementation Date: Tue, 28 Nov 2023 16:09:58 -0500 Message-ID: <20231128211001.877333-9-sashal@kernel.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231128211001.877333-1-sashal@kernel.org> References: <20231128211001.877333-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 4.19.300 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds [ Upstream commit 125b0bb95dd6bec81b806b997a4ccb026eeecf8f ] We really don't want to do atomic_read() or anything like that, since we already have the value, not the lock. The whole point of this is that we've loaded the lock from memory, and we want to check whether the value we loaded was a locked one or not. The main use of this is the lockref code, which loads both the lock and the reference count in one atomic operation, and then works on that combined value. With the atomic_read(), the compiler would pointlessly spill the value to the stack, in order to then be able to read it back "atomically". This is the qspinlock version of commit c6f4a9002252 ("asm-generic: ticket-lock: Optimize arch_spin_value_unlocked()") which fixed this same bug for ticket locks. Cc: Guo Ren Cc: Ingo Molnar Cc: Waiman Long Link: https://lore.kernel.org/all/CAHk-=whNRv0v6kQiV5QO6DJhjH4KEL36vWQ6Re8Csrnh4zbRkQ@mail.gmail.com/ Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- include/asm-generic/qspinlock.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h index 9cc457597ddf8..1a688e5b8b0b5 100644 --- a/include/asm-generic/qspinlock.h +++ b/include/asm-generic/qspinlock.h @@ -47,7 +47,7 @@ static __always_inline int queued_spin_is_locked(struct qspinlock *lock) */ static __always_inline int queued_spin_value_unlocked(struct qspinlock lock) { - return !atomic_read(&lock.val); + return !lock.val.counter; } /** -- 2.42.0