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Received: from willy by casper.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1wedKN-00000005Nc2-1soS; Tue, 30 Jun 2026 18:36:59 +0000 Date: Tue, 30 Jun 2026 19:36:59 +0100 From: Matthew Wilcox To: Gregg Leventhal Cc: "To: Alexander Viro" , Christian Brauner , "Cc: Jan Kara" , Andrew Morton , Song Liu , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Hagberg Subject: Re: Subject: [BUG/RFC] write-open file THP cache purge can discard dirty page cache Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: uj97trgzhxphcioudoit957ymgprmqma X-Rspamd-Queue-Id: 449D880007 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1782844625-407063 X-HE-Meta: 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 9yOsNgjy d98p0EGrP+2q0BKQjU+XVDjKj6ZQ43hL0kFPkHFjcUXmNS/n06rcgKsWTxCV2vtJkZYxi9du+vtU6RgrBxXTMmFZS8kPYcf7SAGbzA8utqSxYGbGF7rV3/s3TYgo/5pRxA6P6anXmTNTeqnA30zER1kf2FseUVpF4tdgP9pV+cDzPto4il9ZmYYS7P976wPJHCVcWhtL/P3U/dt9ynRj0sRMUCEMmuuwJcV7WIUQ8c9dVHb7cu+a2ghDI/RZcFNf2IHNJJlXAz2BWs1F3TTU3plm1X/kYbxoRafmvpjghQauU1kaYXrYWb39CEswSYSRkE09u Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jun 30, 2026 at 01:01:53PM -0400, Gregg Leventhal wrote: > On an affected 6.12 kernel with CONFIG_READ_ONLY_THP_FOR_FS=y, a file can > contain read-only file THPs installed by khugepaged / MADV_COLLAPSE. When that > same file is later opened for write, do_dentry_open() notices > filemap_nr_thps() and drops the page cache: [...] > > This is unsafe if the mapping also contains dirty folios. But there shouldn't be any. It should not be possible to have dirty folios and THPs in the same file unless the filesystem supports large folios natively. If the file is open for writing, the attempt to create THPs should fail.