From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 37765CD343F for ; Fri, 15 May 2026 20:44:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:Message-ID:References:In-Reply-To:Subject:CC:To: From:Date:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=yOPbK2OFF6IcrfoJraZaWua7RTa6T7n9+bq8VLS6qCY=; b=gpYoG7wSo5FZNi2+IYwGX8vSvB /TCAS8XdaE4lmMtmW4/ECTEKr6akG4pCbhmZ3ZRdMtfxEHFf8PkcVK3hwZ6ekzFSWJZZH+NSpJFbw BFaaOUnR6ro265/jGRfNP66M9Az27lsJybzoh4hXLbFGcAaO2XyHON71xBO8j4vEFRO1j1Pe3gux9 qI6Uv9S5IQ0hqaQxUCThc0aQs5/rH5gD3nvbUc2gIxTn0TyYYKP9d5KOSAWqMWV/ULqUIeDbukaIq l5p+wmfFu8/F++WbBbwM1jBHSbRftabMCAm1Y9v237+C/aAH1jh8y3B4XtGIbDrOdvBuANkYs9/Bh p2H/p1qQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wNzOA-00000009P0k-2kHW; Fri, 15 May 2026 20:44:06 +0000 Received: from terminus.zytor.com ([2607:7c80:54:3::136] helo=mail.zytor.com) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wNzO6-00000009Ozg-3SNl; Fri, 15 May 2026 20:44:05 +0000 Received: from ehlo.thunderbird.net (c-76-133-66-138.hsd1.ca.comcast.net [76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 64FJxdt93762934 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Fri, 15 May 2026 12:59:40 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 64FJxdt93762934 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2026042601; t=1778875185; bh=yOPbK2OFF6IcrfoJraZaWua7RTa6T7n9+bq8VLS6qCY=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=HvwBqnLT38+P8wOr09I0oo/MRbA0gltt1BvxpDB/CXoHAI/p9iMtZP4Acni9CBE8i UuQANyZJcLZO9XcaPLGm0i1Xg+soCjS4z5NjIoUETnDDa930DiHBVRAOT/MRlLb9jY QYrQ9QMS7lPYMHGvM8plKfNxe30Gl9az6f+vOCv0hNim3O4/Bdo2qSTnUxGO9V7Nx4 F46aEk0Mx5DZE0TAlF3l22P0Yw61+alulS+V4O2YtDdYTlzt2T6qIuwD2KE0nXfR9T jNDuDCJ8yXY/CId0JmSkw1Ar6+GJQTs5O0RqwrWv5l7cMbOBEgdh93GvzIYQG1gbNB I9HJmsdG2PKng== Date: Fri, 15 May 2026 12:59:34 -0700 From: "H. Peter Anvin" To: Christoph Hellwig , kreijack@inwind.it CC: David Sterba , Andrew Morton , Catalin Marinas , Will Deacon , Ard Biesheuvel , Huacai Chen , WANG Xuerui , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Herbert Xu , Dan Williams , Chris Mason , David Sterba , Arnd Bergmann , Song Liu , Yu Kuai , Li Nan , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-crypto@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-arch@vger.kernel.org, linux-raid@vger.kernel.org Subject: Re: [PATCH 01/19] btrfs: require at least 4 devices for RAID 6 User-Agent: K-9 Mail for Android In-Reply-To: <20260515043705.GA3855@lst.de> References: <20260512052230.2947683-1-hch@lst.de> <20260512052230.2947683-2-hch@lst.de> <20260512114231.GG2558453@suse.cz> <20260513054742.GA1018@lst.de> <0a8d1ff4-f5a2-49e9-aa45-d25dbe4ded40@libero.it> <20260515043705.GA3855@lst.de> Message-ID: <34C16854-1065-4542-8836-DDED58EC1844@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260515_134404_555906_3BDB1C02 X-CRM114-Status: GOOD ( 15.46 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On May 14, 2026 9:37:05 PM PDT, Christoph Hellwig wrote: >On Thu, May 14, 2026 at 09:51:59PM +0200, Goffredo Baroncelli wrote: >> I think that the David concern is : "what happens for an already >> existing btrfs raid6 3 disks filesystem when the user upgrade the kerne= l ?" >> (I am thinking when a new BG needs to be allocated)=2E=2E=2E > >Then it will cleanly fail to mount instead of constantly corrupting data >and memory with every write, yes=2E Which clearly suggest that such >file systems don't exist in the wild=2E > >But if btrfs wants to keep supporting this I'll just add a _unsafe >version without the check in the core library=2E I don't think this is a good idea=2E Error out; it is the btrfs maintainer= s' job to ensure user data isn't lost=2E=20 The RAID-6 code has *never* supported only 3 units, and if it ever worked = for *any* of the implementations it was purely by accident=2E Speaking as t= he original author I should know; this was deliberate as in some cases the = degenerate case (3) would have required extra trays in the code to no user = benefit=2E=20 I would not be surprised if the kernel crashed or corrupted the page cache= in that case=2E