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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 08/10] ceph: convert page cleanup loop in writepages_finish() to folios Message-ID: References: <20260804-remove-wait-on-page-writeback-v2-0-81f0ab065284@columbia.edu> <20260804-remove-wait-on-page-writeback-v2-8-81f0ab065284@columbia.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 2C5EBA0013 X-Stat-Signature: nwsyud8bwd6esetas6mhyeaoys9e7mwu X-Rspam-User: X-HE-Tag: 1785887635-717811 X-HE-Meta: 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 cimyb3nH a+7qzlhrTIBycqa1aKmjb1ZGfcw3conmJ3AR0iWailvVn/Mk4ItQroN4IQK9gOXv0lcM7zLREFVHTJ+FgKVrQEJDhJEnUWbsfOiThZO8MndurLqmsqL/C/z/MGdSNc9v5H3tbly9LKVzag6h0k7ymdXvF1jGQX9MXNGdMF+2IRBW67lDeyVhRYaZzMhJPdcKBtf0Oa/CNOIKbUoUljEZyqQwRh+RbTOLGqOWRj3F14LnN38hGKh5zfyZIFWQt7kisJMJfk1jZY9X1v4EfOLgABKmgnF4M39NGTBgX Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 05, 2026 at 02:33:34AM +0300, Tal Zussman wrote: > > for (j = 0; j < num_pages; j++) { > > + struct folio *folio; > > + > > fscrypt_finalize_bounce_page(&osd_data->pages[j]); > > - page = osd_data->pages[j]; > > - BUG_ON(!page); > > - WARN_ON(!PageUptodate(page)); > > + folio = page_folio(osd_data->pages[j]); > > + BUG_ON(!folio); > > + WARN_ON(!folio_test_uptodate(folio)); > > Sashiko complains: > > "Since page_folio() invokes _compound_head() which dereferences the page > pointer, won't this cause a NULL pointer dereference before reaching the > BUG_ON(!folio) check if osd_data->pages[j] is actually NULL? > The previous code checked the page pointer before any dereference occurred. > Would it be safer to check the array element for NULL before passing it to > page_folio()?" > > The BUG_ON can just be removed, as fscrypt_finalize_bounce_page() cannot take > or set its argument to NULL as constructed, so the check was unnecessary > to begin with. Heh, Sashiko beat me to it ;-) I'd agree, the BUG_ON was always unnecessary, and I was going to recommend just deleting it.