Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755904Ab3JUJZg (ORCPT ); Mon, 21 Oct 2013 05:25:36 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:39437 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753480Ab3JUIvL (ORCPT ); Mon, 21 Oct 2013 04:51:11 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Maxim Patlasov" , "Maxim Patlasov" , "Miklos Szeredi" Date: Mon, 21 Oct 2013 09:46:28 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 048/149] fuse: postpone end_page_writeback() in fuse_writepage_locked() In-Reply-To: X-SA-Exim-Connect-IP: 212.20.242.100 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2437 Lines: 63 3.2.52-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Maxim Patlasov commit 4a4ac4eba1010ef9a804569058ab29e3450c0315 upstream. 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 Signed-off-by: Miklos Szeredi Signed-off-by: Ben Hutchings --- fs/fuse/file.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -1251,7 +1251,6 @@ static int fuse_writepage_locked(struct 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); @@ -1259,6 +1258,8 @@ static int fuse_writepage_locked(struct fuse_flush_writepages(inode); spin_unlock(&fc->lock); + end_page_writeback(page); + return 0; err_free: -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/