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[13.113.80.70]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ccc9bdb7ddsm128255315ad.1.2026.07.14.22.46.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Jul 2026 22:46:59 -0700 (PDT) Message-ID: <4289be1b-285c-4641-a7b6-6b8e66f458c6@gmail.com> Date: Wed, 15 Jul 2026 13:46:56 +0800 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] two raid consistency bugs To: Qu Wenruo , linux-btrfs@vger.kernel.org Cc: David Sterba , Qu Wenruo , Filipe Manana References: <20260714161044.7330-1-zhangboyang.id@gmail.com> <67cff567-1070-4908-a253-a8907d237734@gmx.com> Content-Language: en-US From: Zhang Boyang In-Reply-To: <67cff567-1070-4908-a253-a8907d237734@gmx.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi, On 2026/7/15 05:40, Qu Wenruo wrote: >> At first power failure during transaction N, metadata trees of >> generation N are written to disk A, but super is not committed. Nothing >> is written to disk B. >> >> At second power failure during a different transaction N, > > If it's a different transaction, why it will still have the same transid N? > Because the power failure occurred just before writing superblock (transid N). The superblock on disk still has transid N-1. After reboot, looking at superblock which transid is N-1, btrfs has no idea of transid N existed previously, so it uses transid N for new transcation. >> nothing is >> written to disk A, but metadata trees and super is committed to disk B. >> >> This creates a ambiguous generation N in two disks. Currently btrfs >> can't detect this, and can lead to severe damages. By the way, I came up another solution: If generation mismatch between devices (or log-tree mismatch) is detected at mount time, set a dirty flag in superblock on device which is behind. If dirty flag is set for a device, disable read load balancing for that device. So (meta)data only read from latest device(s). If dirty flag is detected, ask user to run a scrub. The dirty flag is cleared after a successful scrub. Zhang Boyang