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 2A498C43334 for ; Wed, 13 Jul 2022 15:54:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237073AbiGMPy1 (ORCPT ); Wed, 13 Jul 2022 11:54:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59130 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236837AbiGMPyW (ORCPT ); Wed, 13 Jul 2022 11:54:22 -0400 Received: from mail-ej1-x62a.google.com (mail-ej1-x62a.google.com [IPv6:2a00:1450:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AB4C62A717 for ; Wed, 13 Jul 2022 08:54:21 -0700 (PDT) Received: by mail-ej1-x62a.google.com with SMTP id j22so20636960ejs.2 for ; Wed, 13 Jul 2022 08:54:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=ijboKzjTSzsd+bJY8ZcuFW/Xbsztbht17nmFPJI6drg=; b=BAIUjy11tSgwstQ6yLGA9n142er4g913SnNJP7srr8eNQuI5Syjw4vBaYQ3DPcV0S9 ZMFoSB9cQeO+Q8HUEUWWxOMpDv2x4HKLnc1U2DhzE+S7AGsI86d3PJRfM6fU2Imm2O3h azTlWaUG47LcDLgRILUq0aSU1jcIjCwpwJGTJ3f43luwnKc1ndMHdDhhjp/O5zr0+Z3+ 9QVKufP4jfnR9gsXnaE79hesIub45kOKPoofUhpfoKCesv1T9NFAMqgu0dGxD43wyohR vJRBth3JGyq8TWcpIEkKeMjLxRmO4aaTMA+2pm7DP1YbphJSLYuzHdIBPfC9lR/4wozk AI8Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=ijboKzjTSzsd+bJY8ZcuFW/Xbsztbht17nmFPJI6drg=; b=ZwO0IbYA0+bP28sdJxiHM0t99JlkeEdvnUkvm0EfAZlnSvgHBCfm4TKDD/Q+XfF6ev 1FjtSULLZvVFH87Y/SD12zUqvH5k0N15Xq+M0oePIFOwWTwm8WBqajjkzbFLBrZLnrP+ L+dX4YnNwFspK+WYfIGCDQrZZgMcBdiDxriAac+MhLewBXt0FoDwobIi+yD9uEuCawqN NdEk0VTUk2dDBHKCzKPgyAI108h+XMqAVoVduvKLawEv3bAfgv4i5rzM6G8xaQYY2K2L pgG43wxPcxwOulxMOCCBNvue9ItXNNYsN9gFR7aeiN/q5iFI6qOjLlbofsNtMx5u0VAw IV6A== X-Gm-Message-State: AJIora/Of8xhOcgg2ZjGQqmMqnr8Sy/K+6oeBvjAUXCYdjprK5p8zDoS m1CUOahuO0ZMkVqZAzv8crW7Z+AS+P0= X-Google-Smtp-Source: AGRyM1v+EgyXmm+WIrwhqUTLys0FStOlDDH9tqmrDCD2QlygO0YDrLJOW0xQwcLtW4iugGwmqF1VrA== X-Received: by 2002:a17:906:8459:b0:72b:60c8:107d with SMTP id e25-20020a170906845900b0072b60c8107dmr4300159ejy.142.1657727660065; Wed, 13 Jul 2022 08:54:20 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id n2-20020a17090695c200b0072b21cab5a5sm5073688ejy.133.2022.07.13.08.54.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Jul 2022 08:54:19 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , "Eric W. Biederman" Subject: [PATCH 2/2] ucount: Use atomic_long_try_cmpxchg in atomic_long_inc_below Date: Wed, 13 Jul 2022 17:54:05 +0200 Message-Id: <20220713155405.80663-3-ubizjak@gmail.com> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20220713155405.80663-1-ubizjak@gmail.com> References: <20220713155405.80663-1-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 974ac1585009..5d980460104e 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -218,16 +218,14 @@ 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, -- 2.35.3