From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-183.mta0.migadu.com (out-183.mta0.migadu.com [91.218.175.183]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BE67728F1 for ; Mon, 25 Aug 2025 07:47:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.183 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756108022; cv=none; b=pLmtIfzUUPW9+r02cgj6UPWID76z3K3BNSiQOM7/5/qv6hBun1oJEIGUCaJaveAywuuDO3aqTWzfMfVnHemnT1TA3sYuU8T77rp9HSexi2LEl4pjuD/ElIN1EizfU+c6QhtPodFXeA30wQ/ANOWJHyUv/mcX1EHsfV5eHmc4MRc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756108022; c=relaxed/simple; bh=Nbzd19yUjVLxyR4RmsPuP6P/OEWa8peSA4D/Bsvo6QA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XIMBaF2EnQH3GFT3wbAFsKcIu/hMVUjt6RaEjUNB6YJtUo8lQ2rhlhNCC/9I3Zm3q8xjgDCpJAbNjnnIxmL2qtexQQ+XNq+4m6mEWhYzRE8LsZc5h7PJc51eAXpbptcdMSFBe3xMFf0Og/9Vb0gFY4WrWRNymaZMpVk7ksUUtmA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=UjHepv8b; arc=none smtp.client-ip=91.218.175.183 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="UjHepv8b" Message-ID: <4e7e7292-338d-4a57-84ec-ae7427f6ad7c@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1756108009; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QuBezIELdTw6MY40H0rggeYKFrP3ZFapNdPV9JT04jc=; b=UjHepv8bsjSnrSIiGUpmII7coGV4lqLR7tStk3RW3xsbEqWay19GTGYB6hzWxDOPHELs5q Nst0pvGRUNWWzE2c6fJ1+9fMqcRyH+0tknS8BX+KolUbgA6aMS8dzVBlFv4NK3GQBRwdNi VkO8N+/sY7CMZE/kTPsxoMb+areJTRw= Date: Mon, 25 Aug 2025 15:46:42 +0800 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] atomic: Specify natural alignment for atomic_t Content-Language: en-US To: Finn Thain Cc: 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 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <5a44c60b-650a-1f8a-d5cb-abf9f0716817@linux-m68k.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT 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); 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.