From nobody Sun Oct 5 00:09:21 2025 Received: from mail-wr1-f49.google.com (mail-wr1-f49.google.com [209.85.221.49]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 238492D77E4; Mon, 11 Aug 2025 12:53:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.49 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754916800; cv=none; b=nEC+nryJinKeq5R3ovN8XZq4NHcHxNTyXg9YgSMuIq1ajn6IURpVBnaQyzStTwWZ1lC/2YwcoXMBxdMhyooUheRtQlXI1KCzzwM4cU/e5TuYAuuxOGbPkxzYutMqTvfB4OXfZU+JK5a96+LC9qwMhZwQK0kNyrNtLR9yr6wXNSU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754916800; c=relaxed/simple; bh=zBFiHfemwtyvXXsvAMZhx4anhbqrwOkhIvWvpmO2tLY=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=c8ECH5lCqbX5Y5lm1S/JDFUgU24FbRy7HH87NWxw8wIEa682SqhNBjzzEbVJU7RrOVVeII3XuzPc0sDDuPQrB1dYQ5/zs+qtTxG6ILWl8Wk3ATW9W6J9GqJSw9tMCI1KlGiomcM8R1xfOcZfsQfSQA6570ZjLa7sV5K+kH5LBdU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=gLK6GBN8; arc=none smtp.client-ip=209.85.221.49 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="gLK6GBN8" Received: by mail-wr1-f49.google.com with SMTP id ffacd0b85a97d-3b786421e36so2303205f8f.3; Mon, 11 Aug 2025 05:53:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1754916797; x=1755521597; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=4IR9Tj2ZFkHOVuxQAA7y4iVif6p4KRJfjxccWwOTQQE=; b=gLK6GBN8afe23iZgVMeyT5ywKVQ3otg1wgy9YiPKHfisgRdHzP8fXugRPZ1yAR/1v/ CZdSJg4qokpa8p8SEaVXwPlbLYZmjEFuTohO/UD3JmzDoYCdyTa+HULYNw9hRkaEYxPh 0uj/04igBfPJo9qPYq82OgBsIGAftr+dinAR2mFRS+ZO/4G7zACLfV/ykoGxfa6ob6EG s2auNv5/SqpR+XhPDflrKKcGg15YiCR6vE5P3ZhZiMgh8lasI2ceQgD/UqMzCOeph0bf RD6m4de+j4I+qnpI3dGFFZW9STMzcSNFSnazUgMq/f/0m2FUD9iRl93qOw+k9uBy1jRL llxg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1754916797; x=1755521597; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=4IR9Tj2ZFkHOVuxQAA7y4iVif6p4KRJfjxccWwOTQQE=; b=j7J/7POlgXGYzsgg6VfVeD1NY36SzB9LprbcpgvaNxYGZugkRaT75J5x0ZfdV5s2Ey MGwcl2WQ6L6vRs58fArbSdJYbPh8LqrUBMsAZ3WB4ovAIzqGXVmSEY8Spcp7n2jTtTQI haCSX/GI6Jp3H5X0ZNQa799mu6Gxqi0Pb5lkKMURfXjOz3c2H1xU8fg26xSzTHXrKgKl pUu4MP/AWQ6hm3GQkqta2Gp7/bT0ZSeV/4bfX2qjYwSWG8V2ORqaMCXZHQAnajDDTzPn oeyb45xwA0rxBW52UnLw0PDGCZpQ9tvXwr82eVWjMhArtryHEmiPzMR+MAptRl47458O Qr2g== X-Forwarded-Encrypted: i=1; AJvYcCVJtiMa6ngu5Tnii6fZ1EDRwOiBX2jpy3u48N6xbBpy3a5fCRNxsAOLMlcZcaxSiOUsKIqF4iTs5/TyW0Q=@vger.kernel.org X-Gm-Message-State: AOJu0YwP5q+83xpPyeWIM7HM57MkMnNDCj4zYhzSzle2gng6QWZnnh8C qHAdsjYHebkFOvPaiJSohUdNF1E8mLg8he1v0u+v7022w5CtpsLoQqoUT5RNTg== X-Gm-Gg: ASbGncvG60dQPpIOeP5gR8NQMe6O1vA/hgPmeK8JXhfd222UoCs0f6h5Jtl0KejkagI OM0HyHxWC+HO3c3+BFcBzTUgnseeZ3wpyrm1f1+jyAfQhI91MbTzyJThGEkCN/YIBYhst4pD9x5 dLSVeiyOIOS6pP2FNqDJ7mzGA1eOeVm2shzO30wf+zzyftoGciC4SwWV/guOit+GCTPeQ3/nWFA 3z7yrxx5AzCfrdrzz+H4E6Yhhz2ERLM2TrjVsAm0/Y22b7qYypun2z0QSwx6iaL0RxaDBNsVHhF Fb7HBZ5zQPEMow52lnEqzKmvX9XWxZPKmo0MgjP7pwoNIbOce/TTgxa9LYatfeT4GS9SEN/WRJt meGW7W+95gDfpvPJhm2Jf1g== X-Google-Smtp-Source: AGHT+IHwd702a+KQNTgQmvdd5bcelZ8AJusFrlVzmIvThx90Mz4CBzwR/92RC2fBAa15d7QtMUdQzw== X-Received: by 2002:a05:6000:290b:b0:3b7:8fcc:a1e3 with SMTP id ffacd0b85a97d-3b900b5108cmr9189025f8f.48.1754916796691; Mon, 11 Aug 2025 05:53:16 -0700 (PDT) Received: from fedora ([193.77.86.199]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-459e0a24bf1sm277093835e9.1.2025.08.11.05.53.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 11 Aug 2025 05:53:16 -0700 (PDT) From: Uros Bizjak To: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Alexander Viro , Christian Brauner , Jan Kara Subject: [PATCH] fs: Use try_cmpxchg() in start_dir_add() Date: Mon, 11 Aug 2025 14:52:38 +0200 Message-ID: <20250811125308.616717-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Use try_cmpxchg() instead of cmpxchg(*ptr, old, new) =3D=3D old. The x86 CMPXCHG instruction returns success in the ZF flag, so this change saves a compare after CMPXCHG (and related move instruction in front of CMPXCHG). Note that the value from *ptr should be read using READ_ONCE() to prevent the compiler from merging, refetching or reordering the read. No functional change intended. Signed-off-by: Uros Bizjak Cc: Alexander Viro Cc: Christian Brauner Cc: Jan Kara Reviewed-by: Jan Kara --- fs/dcache.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 60046ae23d51..336bdb4c4b1f 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2509,8 +2509,8 @@ static inline unsigned start_dir_add(struct inode *di= r) { preempt_disable_nested(); for (;;) { - unsigned n =3D dir->i_dir_seq; - if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) =3D=3D n) + unsigned n =3D READ_ONCE(dir->i_dir_seq); + if (!(n & 1) && try_cmpxchg(&dir->i_dir_seq, &n, n + 1)) return n; cpu_relax(); } --=20 2.50.1