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From: Kent Overstreet To: Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-bcachefs@vger.kernel.org Subject: Re: bcachefs dropped writes with lockless buffered io path, COMPACTION/MIGRATION=y Message-ID: <2iroae47robod2vijalby64iczk2emltrshmztlwyrxmkeiydd@4lxo55nlgpxo> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: iuh3yib8f5rsi7qarkript6fihyhtszw X-Rspamd-Queue-Id: 8717FA0009 X-Rspamd-Server: rspam11 X-HE-Tag: 1724733392-667707 X-HE-Meta: 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 DqeZc20d nJEZjbAeIr2ImvYIRPaTYqcJKBuuSiziur7WMn/uxBi0m3s0cxts5ffEH0d4s6ArWLrMktVzv3EOkYLmd5bavzJQYt3+OjBwG4rHOkxVXHXVIg8/wu0fqoatKzRdS+5jIum8LflYPRKGsGSvLAuRPOQsrn/mFnH2DdGxTeePgKIMLhB79HgffCtA4HQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 27, 2024 at 04:36:33AM GMT, Matthew Wilcox wrote: > On Mon, Aug 26, 2024 at 11:29:52PM -0400, Kent Overstreet wrote: > > We had a report of corruption on nixos, on tests that build a system > > image, it bisected to the patch that enabled buffered writes without > > taking the inode lock: > > > > https://evilpiepirate.org/git/bcachefs.git/commit/?id=7e64c86cdc6c > > > > It appears that dirty folios are being dropped somehow; corrupt files, > > when checked against good copies, have ranges of 0s that are 4k aligned > > (modulo 2k, likely a misaligned partition). > > > > Interestingly, it only triggers for QEMU - the test fails pretty > > consistently and we have a lot of nixos users, we'd notice (via nix > > store verifies) if the corruption was more widespread. We believe it > > only triggers with QEMU's snapshots mode (but don't quote me on that). > > Just to be crystal clear here, the corruption happens while running > bcachefs in the qemu guest, and it doesn't matter what the host > filesystem is? > > Or did I misunderstand, and it occurs while running anything inside qemu > on top of a bcachefs host? The host is running bcachefs, backing qemu's disk image. (And I'm using nested virtualization for bisecting, it's been a lot to keep straight).