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 14DFBC433FE for ; Mon, 17 Oct 2022 14:41:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230489AbiJQOl1 (ORCPT ); Mon, 17 Oct 2022 10:41:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56374 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230474AbiJQOlY (ORCPT ); Mon, 17 Oct 2022 10:41:24 -0400 Received: from mail-ej1-x632.google.com (mail-ej1-x632.google.com [IPv6:2a00:1450:4864:20::632]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6C7A52455 for ; Mon, 17 Oct 2022 07:41:22 -0700 (PDT) Received: by mail-ej1-x632.google.com with SMTP id 13so25467954ejn.3 for ; Mon, 17 Oct 2022 07:41:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=HuBb5ljQMpmcyaTrGqF1Fy74D+G132DrFCMrIoW3IlA=; b=YfHjKFirxF/uU5tvjOiYI8MDgrsuFH+rzZTctvdHoxu4J5uIvM5uNDryofSIuBCPOS rEc+icCdKPeWSz1RxXEmt/GDRj6VikjonJjpt6v44MXBG0DaB0jpUM0kg/CoZKFGLbme AIyTSw1RRcGoVlElAhPDP9KyGBshifi/VQ2iH/6aH4hWQEvD2rbMbuUeqr1/b5cqOJp9 TQHxZEcyxEdOzX0PNyvZJ0qjJNjxvDNAMD/pQ64OxsaZUnF/BKRt0nekFtLkO8D8FWus ed9aqWODkE/P7db8UCQGjAXBW27ouhAhP9fVZ+W2a6TZZ4S3p43X2/ZBTih/5qYVsOJZ CRkg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=HuBb5ljQMpmcyaTrGqF1Fy74D+G132DrFCMrIoW3IlA=; b=b0eFek+i0BIz+QsrHCH2jmCRxiDwJ/JKuA/3AQJQ5ecs3UhRS7O/gYLitFZq41GGsH HY+vfMD5+mTZ4Rvm0XU5WXmQQFJVzAuIcWlqo3AWAmmfZ0NWD1lEBjRxMqJb9gsRtdMx TnZKMHsFDAKt7ywBELWYfGCSN0I8Hf8FpQVbZoRmHpSutCpn5ETZNhNAaCPnKgtzPgm5 L78ZRtBE2xwLy0FSfnQIgYEmWi31XHOxgQ5nh7W/7uU+Y1I7/AtmJLYwWUrM1/rfn263 MFdWxWYTp3IJT4eUlvzI7/d8DISO5VowXIoVLTE6MFDzYnpxKV8E837KbVNryMH/yufy LC4A== X-Gm-Message-State: ACrzQf1d5P3kF0fMCWHZYNYlnZDyxQy5hyX27z1y7gjW1L5e0IwJcOf2 iITaa70zfex0uBJd5nOq8Nx16Rw+NU+yGg== X-Google-Smtp-Source: AMsMyM6j8xNXHz7nj9oU8cJB2C/2vyCxJUVwOjhzlM3EeEVuD4gmuBM9CitJAFvs8G78oNudvED/YA== X-Received: by 2002:a17:907:70b:b0:740:ef93:2ffb with SMTP id xb11-20020a170907070b00b00740ef932ffbmr8748604ejb.93.1666017680684; Mon, 17 Oct 2022 07:41:20 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id dn2-20020a05640222e200b00459cf672a65sm7469144edb.71.2022.10.17.07.41.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Oct 2022 07:41:20 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , "Eric W. Biederman" Subject: [PATCH RESEND 2/2] ucount: Use atomic_long_try_cmpxchg in atomic_long_inc_below Date: Mon, 17 Oct 2022 16:40:49 +0200 Message-Id: <20221017144049.3404-3-ubizjak@gmail.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221017144049.3404-1-ubizjak@gmail.com> References: <20221017144049.3404-1-ubizjak@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use atomic_long_try_cmpxchg instead of atomic_long_cmpxchg (*ptr, old, new) == old in atomic_long_inc_below. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, atomic_long_try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications. No functional change intended. Signed-off-by: Uros Bizjak Cc: "Eric W. Biederman" --- kernel/ucount.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/kernel/ucount.c b/kernel/ucount.c index 74f5b4959feb..2c04589a61ff 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -214,16 +214,14 @@ void put_ucounts(struct ucounts *ucounts) static inline bool atomic_long_inc_below(atomic_long_t *v, long u) { - long c, old; - c = atomic_long_read(v); - for (;;) { + long c = atomic_long_read(v); + + do { if (unlikely(c >= u)) return false; - old = atomic_long_cmpxchg(v, c, c+1); - if (likely(old == c)) - return true; - c = old; - } + } while (!atomic_long_try_cmpxchg(v, &c, c+1)); + + return true; } struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, -- 2.37.3