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=-5.8 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 41142C433B4 for ; Thu, 13 May 2021 19:39:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 183BE61358 for ; Thu, 13 May 2021 19:39:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230154AbhEMTkx (ORCPT ); Thu, 13 May 2021 15:40:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229803AbhEMTkw (ORCPT ); Thu, 13 May 2021 15:40:52 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C3085C061574; Thu, 13 May 2021 12:39:42 -0700 (PDT) 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=O8VUCTzxVSvxa3wVLPh12tovGUEtpcQQ1uxw15XLCZg=; b=S6oimQ+wSggkHbM04qw7qRcCif KxJ6s1XOGzoOpDq2Ik3+iRiwQfDzyBbe0DuWvzC9OR6jXy0kTrw+5iOA+LaoPKGquDRsAkhwtB1fn RAzftQHw1WIHsSHGyasEKCqK6uNc5md/QTdqO/gAX92LY/xjc3aThySb167Hsk1QbFODw0SI99hZD FJ7grq8hsbbFuQNaq3roe74z070sMG/wQF5s2VcKbYsspDgU3/f5jnSJCnX9ybUtPMZoBzeRLnZAR rt44B26yeOFUgC3PP1bOEdl/6GZRpu188I1tXE0mY9mkIB2XhLxPk/VtnEIL19/rPQgwFkGk1TQkJ GlbkDIiw==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lhHAV-009iZc-F6; Thu, 13 May 2021 19:39:06 +0000 Date: Thu, 13 May 2021 20:38:47 +0100 From: Matthew Wilcox To: Jan Kara Cc: linux-fsdevel@vger.kernel.org, Christoph Hellwig , Dave Chinner , ceph-devel@vger.kernel.org, Chao Yu , Damien Le Moal , "Darrick J. Wong" , Jaegeuk Kim , Jeff Layton , Johannes Thumshirn , linux-cifs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mm@kvack.org, linux-xfs@vger.kernel.org, Miklos Szeredi , Steve French , Ted Tso Subject: Re: [PATCH 03/11] mm: Protect operations adding pages to page cache with invalidate_lock Message-ID: References: <20210512101639.22278-1-jack@suse.cz> <20210512134631.4053-3-jack@suse.cz> <20210513190114.GJ2734@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210513190114.GJ2734@quack2.suse.cz> Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org On Thu, May 13, 2021 at 09:01:14PM +0200, Jan Kara wrote: > On Wed 12-05-21 15:40:21, Matthew Wilcox wrote: > > Remind me (or, rather, add to the documentation) why we have to hold the > > invalidate_lock during the call to readpage / readahead, and we don't just > > hold it around the call to add_to_page_cache / add_to_page_cache_locked > > / add_to_page_cache_lru ? I appreciate that ->readpages is still going > > to suck, but we're down to just three implementations of ->readpages now > > (9p, cifs & nfs). > > There's a comment in filemap_create_page() trying to explain this. We need > to protect against cases like: Filesystem with 1k blocksize, file F has > page at index 0 with uptodate buffer at 0-1k, rest not uptodate. All blocks > underlying page are allocated. Now let read at offset 1k race with hole > punch at offset 1k, length 1k. > > read() hole punch > ... > filemap_read() > filemap_get_pages() > - page found in the page cache but !Uptodate > filemap_update_page() > locks everything > truncate_inode_pages_range() > lock_page(page) > do_invalidatepage() > unlock_page(page) > locks page > filemap_read_page() Ah, this is the partial_start case, which means that page->mapping is still valid. But that means that do_invalidatepage() was called with (offset 1024, length 1024), immediately after we called zero_user_segment(). So isn't this a bug in the fs do_invalidatepage()? The range from 1k-2k _is_ uptodate. It's been zeroed in memory, and if we were to run after the "free block" below, we'd get that memory zeroed again. > ->readpage() > block underlying offset 1k > still allocated -> map buffer > free block under offset 1k > submit IO -> corrupted data > > If you think I should expand it to explain more details, please tell. > Or maybe I can put more detailed discussion like above into the changelog? > > Why not: > > > > __init_rwsem(&mapping->invalidate_lock, "mapping.invalidate_lock", > > &sb->s_type->invalidate_lock_key); > > I replicated what we do for i_rwsem but you're right, this is better. > Updated. Hmm, there's a few places we should use __init_rwsem() ... something for my "when bored" pile of work.