From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 501E1C4742C for ; Mon, 2 Nov 2020 19:03:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F181B22243 for ; Mon, 2 Nov 2020 19:03:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Wdd3QXKd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726430AbgKBTDg (ORCPT ); Mon, 2 Nov 2020 14:03:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35622 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726360AbgKBTDg (ORCPT ); Mon, 2 Nov 2020 14:03:36 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E342BC0617A6 for ; Mon, 2 Nov 2020 11:03:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=iu/ELk0oTaWr4xo8QIwbD6ymrUOmLRRWxZ5jFz+Ejrs=; b=Wdd3QXKdMH77MIOCf67Vxy1WJM CO7erxPwKgcLLjg48twfx39Us8BhYeQTRaWxpBMsYj0XxIkqn7I1McQTxT7DqyaNiS5k7R+Aq0tRi Q5goGoCSDg+gFBKNSKvzCUL3h7qeeQEEXT+megkQrmeMTau2yUE35ZUXLpQ9akJcdyqmCFrVkS6BG U2ijw+9KSqywkdcur3aoNvsST1HDmtnR4QUxugu5KjkX5wFscvlNzIt8RBm37msjx6WTyWoC/4IsB X5B8Y324kteaKfXNbvvlVPyoxTx3GvcsgD9oY0XOGyoe0J7x7hXXsBOORov91ETxxTcrxMwK45Nzi 1TMuXL7w==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kZf78-00088k-FO; Mon, 02 Nov 2020 19:03:34 +0000 Date: Mon, 2 Nov 2020 19:03:34 +0000 From: Matthew Wilcox To: Kent Overstreet Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, hch@lst.de Subject: Re: [PATCH 04/17] mm/filemap: Support readpage splitting a page Message-ID: <20201102190334.GQ27442@casper.infradead.org> References: <20201102184312.25926-1-willy@infradead.org> <20201102184312.25926-5-willy@infradead.org> <20201102190008.GG2123636@moria.home.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201102190008.GG2123636@moria.home.lan> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Nov 02, 2020 at 02:00:08PM -0500, Kent Overstreet wrote: (snipped the deleted lines for clarity) > > if (iocb->ki_flags & IOCB_WAITQ) { > > + error = lock_page_async(page, iocb->ki_waitq); > > + if (error) { > > + put_page(page); > > + return ERR_PTR(error); > > + } > > } else { > > + if (!trylock_page(page)) { > > + put_and_wait_on_page_locked(page, TASK_KILLABLE); > > + return NULL; > > + } > > } > > > > + if (!page->mapping) > > + goto truncated; > > Since we're dropping our ref to the page, it could potentially be truncated and > then reused, no? So we should be checking page->mapping == mapping && > page->index == index (and stashing page->index before dropping our ref, or > passing it in). If we get to this point, then we _didn't_ drop our ref to the page. All the paths above that call put_page() then return.