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 58A0042ABF; Tue, 28 Nov 2023 21:09:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="FPwMKBNT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 40BF4C433C8; Tue, 28 Nov 2023 21:09:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1701205797; bh=u5mztADiX1T2VEvcf4Ybw/rj0X9fGjTqPL9zn4Mv4KM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FPwMKBNTTVoAHLFPDLNrCP7ru4hm62JgobM8x+YImoxfSxu0OCHPVDG9MuW6JGaCS sB66XyoA4JPchfH18gqfIlvQPMy7+Le3wifFm9xPGW+UZfGdWTCBz6T8o68Z1DlKuC fivNIQkSby1sTnwac6jN48dtWU0LoUQ607JaSuLQzBTfwZB0vy9QrA/ZdWf1fbljJu OyLe/gsBcleM3ezY9xPSiYsZc66W1ZAu9QsufdQLdsAsWNHxyAvvOniY9fvtlJGEFf Uz0gkjNZv8zF09IX8yo0l1Pe6b8DlCZbKyLlIOYsWv4z6MZYLyjuvlWJQnCuz+djKS FFnC7I6d+vDyQ== 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 5.4 10/11] asm-generic: qspinlock: fix queued_spin_value_unlocked() implementation Date: Tue, 28 Nov 2023 16:09:34 -0500 Message-ID: <20231128210941.877094-10-sashal@kernel.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231128210941.877094-1-sashal@kernel.org> References: <20231128210941.877094-1-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 5.4.262 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 fde943d180e03..6dc2269a5398a 100644 --- a/include/asm-generic/qspinlock.h +++ b/include/asm-generic/qspinlock.h @@ -38,7 +38,7 @@ 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