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Mon, 15 Dec 2025 19:12:24 -0800 (PST) Date: Tue, 16 Dec 2025 11:12:21 +0800 From: Jinchao Wang To: Matthew Wilcox Cc: Andrew Morton , Christian Brauner , Hannes Reinecke , Luis Chamberlain , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, syzbot+4d3cc33ef7a77041efa6@syzkaller.appspotmail.com, syzbot+fdba5cca73fee92c69d6@syzkaller.appspotmail.com Subject: Re: [PATCH] mm/readahead: read min folio constraints under invalidate lock Message-ID: References: <20251215141936.1045907-1-wangjinchao600@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: C5BCC40006 X-Rspamd-Server: rspam03 X-Stat-Signature: 34eory139qfttb6kzqt8p3zzehnq9i7p X-Rspam-User: X-HE-Tag: 1765854746-49142 X-HE-Meta: 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 Dzv2SgYB 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 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, Dec 16, 2025 at 02:42:06AM +0000, Matthew Wilcox wrote: > On Tue, Dec 16, 2025 at 09:37:51AM +0800, Jinchao Wang wrote: > > On Mon, Dec 15, 2025 at 02:22:23PM +0000, Matthew Wilcox wrote: > > > On Mon, Dec 15, 2025 at 10:19:00PM +0800, Jinchao Wang wrote: > > > > page_cache_ra_order() and page_cache_ra_unbounded() read mapping minimum folio > > > > constraints before taking the invalidate lock, allowing concurrent changes to > > > > violate page cache invariants. > > > > > > > > Move the lookups under filemap_invalidate_lock_shared() to ensure readahead > > > > allocations respect the mapping constraints. > > > > > > Why are the mapping folio size constraints being changed? They're > > > supposed to be set at inode instantiation and then never changed. > > > > They can change after instantiation for block devices. In the syzbot repro: > > blkdev_ioctl() -> blkdev_bszset() -> set_blocksize() -> > > mapping_set_folio_min_order() > > Oh, this is just syzbot doing stupid things. We should probably make > blkdev_bszset() fail if somebody else has an fd open. Thanks, that makes sense. Tightening blkdev_bszset() would avoid the race entirely. This change is meant as a defensive fix to prevent BUGs.