From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9306541C9D; Tue, 28 Nov 2023 21:10:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JCVzU0cd" 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> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 4.19.300 Content-Transfer-Encoding: 8bit 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