From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f47.google.com (mail-wr1-f47.google.com [209.85.221.47]) (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 40DCB2ED164; Mon, 25 Aug 2025 12:07:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.47 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756123641; cv=none; b=eTlWTQrplDnAT70Mx6hoXP2JZ3vsY0+0YIZTwehMWi2H5VZJh6LKrtDEUFERapoVbHaBrWsh/ERRQs4/7+eXX6p8rUjQkuikVvq8XdlvAlbCE9kZyvimDdvq3UQY73xzRURE3rx9W/XJJLlXGLw9gHFSfZJBeah4nO4Bjs5JVyE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756123641; c=relaxed/simple; bh=h5t0F8ZOG4T1UfpMkMbsS1DiLtg8HyKR+2yVoEcpq6M=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=QiT4kzCq1dSTsF5iiuOUpJVbsWbxdWPk/2EWF/bjUddtyegjEwHiNgLL4RMrZeGIzR4yIA9PJQqtaNWMTwoaVXxJniwZWlRSWcDdb3oU/fv5MOFR0XUelSaedUb45Tai8ffldSpRhqw5dNIGvNigzwoZ+DRPLI4h9jXaT8O5UR0= 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=CNW675k5; arc=none smtp.client-ip=209.85.221.47 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="CNW675k5" Received: by mail-wr1-f47.google.com with SMTP id ffacd0b85a97d-3c7aa4ce85dso923572f8f.3; Mon, 25 Aug 2025 05:07:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1756123637; x=1756728437; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=mX6ZyNPbUTtrcs9lMZu6//5EKcjRnkQut+eqn8r6GFM=; b=CNW675k5W4d8yTIuohYwfyld2S7eyHutY1pVvJwUfbdctQ3IftvmJrcI6W+77yV8og KSVTG9IP3uFHlzJkMeHm1QCKsH+akwXMocUgTlKLyxney7Gs68MFRmRno88j463gPPFD NHY1CpOBcNdU0GaiMZftj0KJNNMKARKT1M6fAfRmr9RLBl2DTl1ZqykbKDpHyvWssabY jZb+8bjY5f6dYWhfRcu2yYq2uZDL2HmhWS0Ay9DNC1c7MwmX8OylutgcqhopWkvYIpcU pCTjlgYO67qs3A9qcpm/JXN9DOm9E2luqwgEQhlRvWZNyGbGc+6ZHfK+9lS0hSZsNd8q 09YQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1756123637; x=1756728437; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=mX6ZyNPbUTtrcs9lMZu6//5EKcjRnkQut+eqn8r6GFM=; b=HVcTo3s1Dqe1XqnoFEp0bUaoPw2oxWwXV5dK0FyqalELuFPPKro/lVspU0BZGzAgyc j+DsRey9EIfCc1/MePxqD2HBZEgdSs6DSMEw01CF3eUualJF598PzRxkrqcgtYrFqgVE XRJGBZ5rw5a2tSDOFXtDupusV1npFA0Zz9oshyOds1c1EWaXTzX3iXnuT+V3xrtXaH2R lzAvTduClP2cxo/hE4+ziTQdW256UKVA/0y1+c3278STL/2TORC2OTdJAKoykwkmGeHX cR4SO0ckvNi8uTUPcRCgotv8GtFySeG0vlTMcDE95M5I3JKUosBel3LI1ajfuCvUWMUP f0ng== X-Forwarded-Encrypted: i=1; AJvYcCVRrr3kalI9W8395UvzNIvIBlr1VB0W/47pspmss9tKjBl9ksR7+fmEaNaS+xkLvOvj9mg2TuXF@vger.kernel.org, AJvYcCXDew4YCIBG+LXvfK55kHXJ01pM09k0939aozZvIRlb4dyxYFSTJUYgB5p3L4E2U5JZ5g9MWslr0vg4qjA=@vger.kernel.org X-Gm-Message-State: AOJu0YwKEnovlaYzg1fDg8q0TRjxgFz2wCYZn72912FO4uTVukesZsZr nCZNRUGAUtOEh1HprfWM5KiAmuA1S2enYjGOA1gEEKeP7Hjw9SlhsJrf X-Gm-Gg: ASbGncu/tPaOhJwlirLTnHqLWHlVX9aZIeo1ZZdIX3iRMHuiwZMhM4lXAvzKrqi4lqR ojy/zLAlw/dIOpHgQQu36VKVa78rerZfkvVLoB8BE9f61646c89aHkIAgU+7rlFzKqpPBtbn4O1 3vFZvh4La5rw3+ugz3ovFfqwrzMRwhCEba5QquNlAQDycfYp8BF3MjJCtTru3tWo1HeZM9Ngh4c X7OOnktK088Sk045WEahvigGPytDg1g0kYCRBIhvVtqQhrVGSKyeRbVeiVVIXuDcI6swvoZrVVH JTQWHwtXw8azGENWWvvvMC50l5PhuXo7sNz7fxorgc4WBJsAHysVbV5jw0+Y7d1lpnfu7q56sTx LMYHjtcCs5C+WvjdrCcpOm0dh05wiHruzWcRnUAT3dc+bMc0gYnNEfDEOPfHS/mwW X-Google-Smtp-Source: AGHT+IGeHwM+hA/mxAmVkchgVF32pBoquHDVMxwsrm1PZwKBjfQEV8lVUD0pWP7jEQEySlDA0Z3+rQ== X-Received: by 2002:a5d:5f8d:0:b0:3c7:44eb:dd7f with SMTP id ffacd0b85a97d-3c744ebe1f7mr5834987f8f.18.1756123637228; Mon, 25 Aug 2025 05:07:17 -0700 (PDT) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3c7119c4200sm11243925f8f.53.2025.08.25.05.07.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Aug 2025 05:07:16 -0700 (PDT) Date: Mon, 25 Aug 2025 13:07:15 +0100 From: David Laight To: Lance Yang Cc: Finn Thain , akpm@linux-foundation.org, geert@linux-m68k.org, linux-kernel@vger.kernel.org, mhiramat@kernel.org, oak@helsinkinet.fi, peterz@infradead.org, stable@vger.kernel.org, will@kernel.org, Lance Yang Subject: Re: [PATCH] atomic: Specify natural alignment for atomic_t Message-ID: <20250825130715.3a1141ed@pumpkin> In-Reply-To: <4e7e7292-338d-4a57-84ec-ae7427f6ad7c@linux.dev> References: <7d9554bfe2412ed9427bf71ce38a376e06eb9ec4.1756087385.git.fthain@linux-m68k.org> <20250825032743.80641-1-ioworker0@gmail.com> <96ae7afc-c882-4c3d-9dea-3e2ae2789caf@linux.dev> <5a44c60b-650a-1f8a-d5cb-abf9f0716817@linux-m68k.org> <4e7e7292-338d-4a57-84ec-ae7427f6ad7c@linux.dev> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 25 Aug 2025 15:46:42 +0800 Lance Yang wrote: > On 2025/8/25 14:17, Finn Thain wrote: > > > > On Mon, 25 Aug 2025, Lance Yang wrote: > > > >> > >> What if we squash the runtime check fix into your patch? > > > > Did my patch not solve the problem? > > Hmm... it should solve the problem for natural alignment, which is a > critical fix. > > But it cannot solve the problem of forced misalignment from drivers using > #pragma pack(1). The runtime warning will still trigger in those cases. > > I built a simple test module on a kernel with your patch applied: > > ``` > #include > #include > > struct __attribute__((packed)) test_container { > char padding[49]; > struct mutex io_lock; > }; > > static int __init alignment_init(void) > { > struct test_container cont; > pr_info("io_lock address offset mod 4: %lu\n", (unsigned long)&cont.io_lock % 4); Doesn't that give a compilation warning from 'taking the address of a packed member'? Ignore that at your peril. More problematic is that, IIRC, m68k kmalloc() allocates 16bit aligned memory. This has broken other things in the past. I doubt that increasing the alignment to 32bits would make much difference to the kernel memory footprint. David > return 0; > } > > static void __exit alignment_exit(void) > { > pr_info("Module unloaded\n"); > } > > module_init(alignment_init); > module_exit(alignment_exit); > MODULE_LICENSE("GPL"); > MODULE_AUTHOR("x"); > MODULE_DESCRIPTION("x"); > ``` > > Result from dmesg: > [Mon Aug 25 15:44:50 2025] io_lock address offset mod 4: 1 > > As we can see, a packed struct can still force the entire mutex object > to an unaligned address. With an address like this, the WARN_ON_ONCE > can still be triggered. > > That's why I proposed squashing the runtime check fix into your patch. > Then it can be cleanly backported to stop all the spurious warnings at > once. > > I hope this clarifies things. > >