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 D3506C43334 for ; Thu, 14 Jul 2022 18:28:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240666AbiGNS2k (ORCPT ); Thu, 14 Jul 2022 14:28:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44906 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240665AbiGNS2i (ORCPT ); Thu, 14 Jul 2022 14:28:38 -0400 Received: from mail-ed1-x530.google.com (mail-ed1-x530.google.com [IPv6:2a00:1450:4864:20::530]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1418EDEC for ; Thu, 14 Jul 2022 11:28:35 -0700 (PDT) Received: by mail-ed1-x530.google.com with SMTP id w12so3474651edd.13 for ; Thu, 14 Jul 2022 11:28:34 -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:mime-version :content-transfer-encoding; bh=xJ2AUNFNB80WWdT50P/7IdU+X0ACPCIJDlt+b//8fYY=; b=WRlWIiUkK8ix+c+Ycog1wxs1dRSPzbSp+7maDrC9ESMRa073tPZXjTSzWz57YN921p 5kuX9H42GYUU1Hyx2k/vf/cF7QV/8ZVfzNRMzr0d442YEhGjmhRFjac4mZrmrYPHdfAM nXMUxzlf0JnxgCLKYrorE7ALHy01xt90m9wCv9jSXMxK3dWNIFFqdDm15uY16mLJedrR ApXYZ9qaQtdA2gGUY/8+5CuPgJKWFkVGH4Ur7h4zbS8b8tULf4p8sboVT0CMk+OHjeqJ 3jQ0sWnxuxFjKY88PJBfzSaAqOcBuaTj/9dXxCOItznv3oWXjGVFkpdG8L8lntT9rwIH OThA== 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:mime-version :content-transfer-encoding; bh=xJ2AUNFNB80WWdT50P/7IdU+X0ACPCIJDlt+b//8fYY=; b=L3r/VsT/DruCZR81xJLB/uyLrhYqshFSASJ32STH+Wgk93/5EJRlGBpEmqZWgSv8ZV QFD7KSnVIZbdFQ3KAink2IwOlWJvHajtt0RkEBE6IyRCzE3E7f6xgP+PMWNwb9KrVPKD 0deg5D9biZKtPRKxyqXVrINTJA6djGv0K0q2rH2DFUQ0uVqL/3ZdyIyfrJRPrFTvQJBx MO7pb7XAUdYcCkDlVH1wMcCPjBdF2FOgee6cSsutHVF+L6FN2w016MDssL0bbthxLUzr UGddnzayPNtyfNa2V2lDjHYardmsEnCR0IljDGZqL/3nTi+R694fCGBM4WdqADpSRoJJ Vx6Q== X-Gm-Message-State: AJIora+IziLZZ05USRgWgWhowrks+A78dkz1yIWsZQrWz3O+knr76GlK mmM6Xv3rEwYvNUimjMs3hRZIfQO8/aE= X-Google-Smtp-Source: AGRyM1sKgUj9oHiswxGdwNYZmLWmPRKcZQehdRk6Bw/1asSDIUGmWR6+kjGOeRMgr/5S3IyQQHWQ8w== X-Received: by 2002:a05:6402:50d2:b0:43a:8487:8a09 with SMTP id h18-20020a05640250d200b0043a84878a09mr14054473edb.232.1657823313392; Thu, 14 Jul 2022 11:28:33 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id f24-20020a056402005800b0043a7404314csm1495045edu.8.2022.07.14.11.28.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 Jul 2022 11:28:33 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , "Theodore Ts'o" , "Jason A. Donenfeld" Subject: [PATCH] random: Use try_cmpxchg in _credit_init_bits Date: Thu, 14 Jul 2022 20:28:22 +0200 Message-Id: <20220714182822.25142-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in _credit_init_bits. 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, 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: "Theodore Ts'o" Cc: "Jason A. Donenfeld" --- drivers/char/random.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index e3dd1dd3dd22..78e690f0f9f6 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -643,10 +643,10 @@ static void __cold _credit_init_bits(size_t bits) add = min_t(size_t, bits, POOL_BITS); + orig = READ_ONCE(input_pool.init_bits); do { - orig = READ_ONCE(input_pool.init_bits); new = min_t(unsigned int, POOL_BITS, orig + add); - } while (cmpxchg(&input_pool.init_bits, orig, new) != orig); + } while (!try_cmpxchg(&input_pool.init_bits, &orig, new)); if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) { crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */ -- 2.35.3