From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754966Ab3H2Q1O (ORCPT ); Thu, 29 Aug 2013 12:27:14 -0400 Received: from mail-lb0-f169.google.com ([209.85.217.169]:61641 "EHLO mail-lb0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753060Ab3H2Q1N (ORCPT ); Thu, 29 Aug 2013 12:27:13 -0400 MIME-Version: 1.0 X-Originating-IP: [86.59.245.170] In-Reply-To: <20130812163906.10366.29310.stgit@maximpc.sw.ru> References: <20130812163739.10366.64896.stgit@maximpc.sw.ru> <20130812163906.10366.29310.stgit@maximpc.sw.ru> Date: Thu, 29 Aug 2013 18:27:11 +0200 Message-ID: Subject: Re: [PATCH 1/2] fuse: postpone end_page_writeback() in fuse_writepage_locked() From: Miklos Szeredi To: Maxim Patlasov Cc: fuse-devel , Brian Foster , Kernel Mailing List , devel@openvz.org, Pavel Emelianov Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 12, 2013 at 6:39 PM, Maxim Patlasov wrote: > The patch fixes a race between ftruncate(2), mmap-ed write and write(2): > > 1) An user makes a page dirty via mmap-ed write. > 2) The user performs shrinking truncate(2) intended to purge the page. > 3) Before fuse_do_setattr calls truncate_pagecache, the page goes to > writeback. fuse_writepage_locked fills FUSE_WRITE request and releases > the original page by end_page_writeback. > 4) fuse_do_setattr() completes and successfully returns. Since now, i_mutex > is free. > 5) Ordinary write(2) extends i_size back to cover the page. Note that > fuse_send_write_pages do wait for fuse writeback, but for another > page->index. > 6) fuse_writepage_locked proceeds by queueing FUSE_WRITE request. > fuse_send_writepage is supposed to crop inarg->size of the request, > but it doesn't because i_size has already been extended back. > > Moving end_page_writeback to the end of fuse_writepage_locked fixes the race > because now the fact that truncate_pagecache is successfully returned infers > that fuse_writepage_locked has already called end_page_writeback. And this, > in turn, infers that fuse_flush_writepages has already called > fuse_send_writepage, and the latter used valid (shrunk) i_size. write(2) > could not extend it because of i_mutex held by ftruncate(2). > > Signed-off-by: Maxim Patlasov Applied this, too. Thanks, Miklos > --- > fs/fuse/file.c | 3 ++- > 1 files changed, 2 insertions(+), 1 deletions(-) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 5c121fe..d1715b3 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -1529,7 +1529,6 @@ static int fuse_writepage_locked(struct page *page) > > inc_bdi_stat(mapping->backing_dev_info, BDI_WRITEBACK); > inc_zone_page_state(tmp_page, NR_WRITEBACK_TEMP); > - end_page_writeback(page); > > spin_lock(&fc->lock); > list_add(&req->writepages_entry, &fi->writepages); > @@ -1537,6 +1536,8 @@ static int fuse_writepage_locked(struct page *page) > fuse_flush_writepages(inode); > spin_unlock(&fc->lock); > > + end_page_writeback(page); > + > return 0; > > err_free: >