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Wong" Cc: Carlos Maiolino , xfs , willy@infradead.org, linux-mm@kvack.org Subject: Re: [PATCH] xfs: compute buffer address correctly in xmbuf_map_backing_mem Message-ID: References: <20250408003030.GD6283@frogsfrogsfrogs> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250408003030.GD6283@frogsfrogsfrogs> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: CBB1CC0007 X-Stat-Signature: t8y8cbdre1ku4s7huyasiwte1s39wi8e X-HE-Tag: 1744089069-48429 X-HE-Meta: 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 wGynm9RO 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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 Mon, Apr 07, 2025 at 05:30:30PM -0700, Darrick J. Wong wrote: > From: Darrick J. Wong > > Prior to commit e614a00117bc2d, xmbuf_map_backing_mem relied on > folio_file_page to return the base page for the xmbuf's loff_t in the > xfile, and set b_addr to the page_address of that base page. > > Now that folio_file_page has been removed from xmbuf_map_backing_mem, we > always set b_addr to the folio_address of the folio. This is correct > for the situation where the folio size matches the buffer size, but it's > totally wrong if tmpfs uses large folios. We need to use > offset_in_folio here. > > Found via xfs/801, which demonstrated evidence of corruption of an > in-memory rmap btree block right after initializing an adjacent block. Hmm, I thought we'd never get large folios for our non-standard tmpfs use. I guess I was wrong on that.. The fix looks good: Reviewed-by: Christoph Hellwig But a little note below: > + bp->b_addr = folio_address(folio) + offset_in_folio(folio, pos); Given that this is or at least will become a common pattern, do we want a mm layer helper for it?