From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 3620C1BC41; Thu, 18 Dec 2025 07:14:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766042044; cv=none; b=iRWJCse2kwlcOu8PWImHSlazCmQPTYRZTrrfLPAlK2q5F3egXrVLSnSiz/z0ERZftXPpLTAluhNUmAFf5Pp7rL1wGNFVZQdKhvJdl1hoFA9Fb/Z966ncT8lp5HBTlJgk9hu1lDaCWtub3VjyaxIgSR7LvdSijl0u5Nr7JDDyq5k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766042044; c=relaxed/simple; bh=07jxoBjWTtDHJh4vv6be10PJ3A4HCvArOnIeflRk4EM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=G1TMQ8MsdkvX4y17+mXtmFZVOGLQOIjX1JdFSFld8V5bnFcEvL7W365laQEvyXeIZbYNtVpWKeJxn2yk38fZM+0KJxVzUPIWPvN1BAbjOMeqrLD6EOmIpnqCfytc0avqA8DnbzmejCGr0jlRiF64RlTXZfdUfIVBYegczzYXOqA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=r9p3ghC0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="r9p3ghC0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4EB5BC4CEFB; Thu, 18 Dec 2025 07:14:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1766042043; bh=07jxoBjWTtDHJh4vv6be10PJ3A4HCvArOnIeflRk4EM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=r9p3ghC0xbiDjib5DjReLMCbVxeXMK/7zu/PSM4qJ3BwTAED7KnZL23vOgTubv9+E Cc+RKEZAQX2fR7K86EHCz638aRXneUGpklw/Z3+WrybZK00ETI2rpqd9g8otfOSESk VZYA/SHw7Tp2dtoKDkYPhUBz8tNuh4VuTxPIaDZc= Date: Thu, 18 Dec 2025 08:14:00 +0100 From: Greg KH To: Li Nan Cc: Roman Mamedov , Yu Kuai , stable@vger.kernel.org, song@kernel.org, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, yangerkun@huawei.com, yi.zhang@huawei.com Subject: Re: [PATCH stable/6.18-6.17] md: add check_new_feature module parameter Message-ID: <2025121849-moonlit-emotion-41ed@gregkh> References: <20251217130513.2706844-1-linan666@huaweicloud.com> <2025121700-pedicure-reckless-65b9@gregkh> <6979cd43-d38c-477d-857c-8d211bc85474@fnnas.com> <20251217223130.1c571fa5@nvm> <2025121800-doorframe-enviably-56d5@gregkh> Precedence: bulk X-Mailing-List: linux-raid@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Dec 18, 2025 at 02:57:23PM +0800, Li Nan wrote: > > > 在 2025/12/18 14:30, Greg KH 写道: > > On Wed, Dec 17, 2025 at 10:31:30PM +0500, Roman Mamedov wrote: > > > On Thu, 18 Dec 2025 01:11:43 +0800 > > > "Yu Kuai" wrote: > > > > > > > Hi, > > > > > > > > 在 2025/12/17 22:04, Greg KH 写道: > > > > > On Wed, Dec 17, 2025 at 09:05:13PM +0800, linan666@huaweicloud.com wrote: > > > > > > From: Li Nan > > > > > > > > > > > > commit 9c47127a807da3e36ce80f7c83a1134a291fc021 upstream. > > > > > > > > > > > > Raid checks if pad3 is zero when loading superblock from disk. Arrays > > > > > > created with new features may fail to assemble on old kernels as pad3 > > > > > > is used. > > > > > > > > > > > > Add module parameter check_new_feature to bypass this check. > > > > > This is a new feature, why does it need to go to stable kernels? > > > > > > > > > > And a module parameter? Ugh, this isn't the 1990's anymore, this is not > > > > > good and will be a mess over time (think multiple devices...) > > > > > > > > Nan didn't mention the background. We won't backport the new feature to stable > > > > kernels(Although this fix a data lost problem in the case array is created > > > > with disks in different lbs, anyone is interested can do this). However, this > > > > backport is just used to provide a possible solution for user to still assemble > > > > arrays after switching to old LTS kernels when they are using the default lbs. > > > > > > This is still a bad scenario. Original problem: > > > > > > - Boot into a new kernel once, reboot into the old one, the existing array no > > > longer works. > > > > > > After this patch: > > > > > > - Same. Unless you know how, where and which module parameter to add, to > > > be passed to md module on load. Might be not convenient if the root FS > > > didn't assemble and mount and is inaccessible. > > > > > > Not ideal whatsoever. > > > > > > Wouldn't it be possible to implement minimal *automatic* recognition (and > > > ignoring) of those newly utilized bits instead? > > > > Yes, that should be done instead. > > > > And again, a module parameter does not work for multiple devices in a > > system, the upstream change should also be reverted. > > > > thanks, > > > > greg k-h > > > > . > > We propose the following fix for this issue. After fix, md arrays created > on old kernels won't be affected by this feature. > > https://lore.kernel.org/linux-raid/825e532d-d1e1-44bb-5581-692b7c091796@huaweicloud.com/T/#mb205fb97ab4af629cae9db8dfd236ceaa93f14ad > > The method is: > > only set lbs by default for new array, for assembling the array still > > left the lbs field unset, in this case the data loss problem is not fixed, > > we should also print a warning and guide users to set lbs to fix the > problem, > > with the notification the array will not be assembled in old kernels. Great, have a patch for this? thanks, greg k-h