From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f52.google.com (mail-wr1-f52.google.com [209.85.221.52]) (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 721CE3DDDCA for ; Thu, 6 Aug 2026 08:32:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786005178; cv=none; b=I/QbrGyIDGWrZKmkwlRIrPHhtw9kptCWxJCsnF0SywFInz5rS8+hzK003V0QXKlTBHCnIOgY1aksklsp2qAARA597rawh22w1MjjjMqARlaVom/9xZKaw5hRyT0KWUK97SIF6ReRtD/BA2m1nDwAv0u3ykPpf9Kx8VbLPAw4fKk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786005178; c=relaxed/simple; bh=a8S7/JFgNnijj79KFMHsJp0QhSQmc5cbmCjp8MdJIz4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=p+JRZc6C0XbZ6JRLHfHnpmtXgY/Dxxqaw8kk1ArRfuMAo/z/jBIdXsPYs+7mC8i0NqS8YyVS3hrcM5HR/iK3HkiEidWTR1/9h9XjeXrvkOui4O7pUIbMADM5MQUENmxn/MjDFZZQy36V+sDBt2oueBsMj8AL8mgYbTxO9ryK8KA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=TsTigD0/; arc=none smtp.client-ip=209.85.221.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="TsTigD0/" Received: by mail-wr1-f52.google.com with SMTP id ffacd0b85a97d-47fde295992so554822f8f.0 for ; Thu, 06 Aug 2026 01:32:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1786005172; x=1786609972; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=a8S7/JFgNnijj79KFMHsJp0QhSQmc5cbmCjp8MdJIz4=; b=TsTigD0/XPbfkWE22/1rFlVGn1dDgZHbprne7m2tTdo0sXWTL8TMNZVUJQuzpIXmyH OpKgEP083D7pWnDzI4B3B0ZZ2LCoB1UrZtuEOfOSZjgDJotb2z/R9qpzOuDRm5NDOzXh fiQ3KhNiIi/OXrpNDINseyrWh7OuiLnkLf9SfOOWe0Xd2O4WP1oPJA+ha7ySHBoo1JQX szvAKJYqDZBcwvKcCR39cxWSL8/Siv1qCV5MmyoW/6dZKDN1J5oOo0GM8PhLFdMMkgR6 tVj+kzY8SzUKZp7J0oFC4CXh5SRcrtqz1ghGV86XCMwSeK8UPKzYn3JhB4uan2pGPRdy 4AiQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786005172; x=1786609972; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=a8S7/JFgNnijj79KFMHsJp0QhSQmc5cbmCjp8MdJIz4=; b=FjFHrthVCyszKL3T6ZSRT/YpRkUnr37K+VmI1ygkMijCDb2NtA6OXh/73t9mw1+mid BlbCSvfCr6MGj0u//W3guMQe7V0tDB+RaWRdVNSWx6qJ0qR7FT4dKUDRBBE1iuTGiMpv LShNiku3UueEKAxZKIE3kmDCtKGRExHcU1m/KxAI7S6qS+XkfTyD0BXbjwB1+vESuMWQ t/EhhK8eJm64cEuELVuSkzcqdeiuoR6zLwmVyT0IQ5K9G8llsv6/dJho3FCB7tAWNDa8 T90Z8iCg6XNvJ8mEvb5x8dwpnKpCfDDV/GY4oQxqJ8Dl7pZsLR7okz3lXZ/8Dm7Gl1NN 7Ezg== X-Forwarded-Encrypted: i=1; AHgh+RpXisDv19f+dDhy5zdz/ls+0yKixR00aYblxPYH71GkwnxzRbkHlepfPnnm3tQE5U3ygYFUhXzB2tqem5XocR0=@vger.kernel.org X-Gm-Message-State: AOJu0YwowXzWsg+aWxbLZ+R3BotsmE2eiDqN12Mhj0yvIfhY9/mt+O3W nF3kr5vyZ28qdl5/TW0Qy5T107TLs63NsSRgF3FIrXdArBISRKrTUk24dLuiB/tKWtihQ4I2lXb L5VusK6ZRSg== X-Gm-Gg: AR+sD13vSkdkla37sS9jrzL00CLPWzliGxlfuGnGXa26X4bnO0o+CPyN3a2YxB5F3JN 7m2lMVWVF6ZFyMk6jQi+xJyDgJjt7sQTkElAHAmZo+sgcSLL3LrdNhQOJWStBBaTFh3h/DmNvF5 qrJD9Qz7dNnYFG71qtEXYYimcIXxzaXNMdxWgyYu3YcP+nY0k98BOaiUQtUykvinLiganTK9vN1 XH8oi1mAbANnaBHiWK+yC21fgjoAXxUbKTf7q/ISlgcggJ5um/1VFkPAsGausdTthzoDv3eYa3/ 2oktyvBxyoHVSWTz/qIz8AoFskCx7l4xgTx5SR8OeAsmnpN+y72M4ex8yH32b7RabZ57Kc9EMrn HQimObEfTfj6cOPbXt3zrAxlCdunAa8DAO6fooA51jjwAX0hmYVT3syTkHs5DZ2cp+Zt/wI3sUo kffWA87HgyBrb8a+2wRU/bl8VwIDefdlT8Y+yyvsrXOAKIFRUyQLhk+II+c1souQCO X-Received: by 2002:a05:6000:2893:b0:47f:8abb:1fd2 with SMTP id ffacd0b85a97d-47ff4ba8c30mr7832158f8f.3.1786005171925; Thu, 06 Aug 2026 01:32:51 -0700 (PDT) Received: from localhost.localdomain ([2001:af0:8000:1409:193:86:92:181]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47ff79a7258sm4332220f8f.3.2026.08.06.01.32.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2026 01:32:51 -0700 (PDT) Date: Thu, 6 Aug 2026 10:32:49 +0200 From: Michal =?utf-8?Q?Koutn=C3=BD?= To: Wilson Felipe Pereira Cc: Johannes Weiner , Yosry Ahmed , Nhat Pham , Chengming Zhou , Tejun Heo , Shuah Khan , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH 2/2] selftests/cgroup: test_zswap: fix implicit unsigned promotion bug in test_no_kmem_bypass Message-ID: References: <20260804042053.56940-1-wfelipe@google.com> <20260804042053.56940-3-wfelipe@google.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="lcbrsqi5muuudvb7" Content-Disposition: inline In-Reply-To: <20260804042053.56940-3-wfelipe@google.com> --lcbrsqi5muuudvb7 Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH 2/2] selftests/cgroup: test_zswap: fix implicit unsigned promotion bug in test_no_kmem_bypass MIME-Version: 1.0 On Tue, Aug 04, 2026 at 04:20:45AM +0000, Wilson Felipe Pereira wrote: > In test_no_kmem_bypass(), delta (stored_pages * page_size - zswapped) is > checked against stored_pages * page_size / 4 to verify that the pages > pushed to zswap belong to the test memory cgroup. >=20 > Due to slight stat update timing differences, delta can evaluate to a sma= ll > negative number (e.g. -5MB out of 1GB). Because delta is declared as a > signed int and stored_pages is an unsigned size_t, C's usual arithmetic > conversions implicitly promote a negative delta to a large unsigned 64-bit > integer, causing `delta < stored_pages * page_size / 4` to falsely evalua= te > to 0 and fail the test. Thanks for the breakdown. > Fix this by checking abs(delta), ensuring the test correctly compares the > absolute difference between system zswap and cgroup zswapped bytes. I still think the delta quantity has some meaning here and taking the abs() changes the semantics of the checked inequality. What about making both zswapped and delta `long`s? (Under similar reasoning, there's already a possible loss after squashing cg_read_key_long() result into the `int`.) In any way, also Fixes: a549f9f31561a ("selftests: cgroup: add test_zswap with no kmem bypas= s test") Thanks, Michal --lcbrsqi5muuudvb7 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iJEEABYKADkWIQRCE24Fn/AcRjnLivR+PQLnlNv4CAUCanRGrBsUgAAAAAAEAA5t YW51MiwyLjUrMS4xMiwyLDIACgkQfj0C55Tb+AjG7wEAubwExH9IrXsRlyXqhce7 oitcuCe9bJ98x6HC+nOhwGYBAP1BPxXMx8oSYQJbEG2gUmqt3VXQUyW00jKZMzWe GagA =B29m -----END PGP SIGNATURE----- --lcbrsqi5muuudvb7--