From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758263AbcC2UJm (ORCPT ); Tue, 29 Mar 2016 16:09:42 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:45205 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758067AbcC2UE5 (ORCPT ); Tue, 29 Mar 2016 16:04:57 -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, "David Woodhouse" , "=?UTF-8?Q?Szab=C3=B3=20?= =?UTF-8?Q?Tam=C3=A1s?=" , "Thomas Betker" Date: Tue, 29 Mar 2016 20:18:22 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 38/62] jffs2: Fix page lock / f->sem deadlock In-Reply-To: X-SA-Exim-Connect-IP: 213.146.164.225 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 3.2.79-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: David Woodhouse commit 49e91e7079febe59a20ca885a87dd1c54240d0f1 upstream. With this fix, all code paths should now be obtaining the page lock before f->sem. Reported-by: Szabó Tamás Tested-by: Thomas Betker Signed-off-by: David Woodhouse Signed-off-by: Ben Hutchings --- fs/jffs2/README.Locking | 5 +---- fs/jffs2/gc.c | 17 ++++++++++------- 2 files changed, 11 insertions(+), 11 deletions(-) --- a/fs/jffs2/README.Locking +++ b/fs/jffs2/README.Locking @@ -2,10 +2,6 @@ JFFS2 LOCKING DOCUMENTATION --------------------------- -At least theoretically, JFFS2 does not require the Big Kernel Lock -(BKL), which was always helpfully obtained for it by Linux 2.4 VFS -code. It has its own locking, as described below. - This document attempts to describe the existing locking rules for JFFS2. It is not expected to remain perfectly up to date, but ought to be fairly close. @@ -69,6 +65,7 @@ Ordering constraints: any f->sem held. 2. Never attempt to lock two file mutexes in one thread. No ordering rules have been made for doing so. + 3. Never lock a page cache page with f->sem held. erase_completion_lock spinlock --- a/fs/jffs2/gc.c +++ b/fs/jffs2/gc.c @@ -1246,14 +1246,17 @@ static int jffs2_garbage_collect_dnode(s BUG_ON(start > orig_start); } - /* First, use readpage() to read the appropriate page into the page cache */ - /* Q: What happens if we actually try to GC the _same_ page for which commit_write() - * triggered garbage collection in the first place? - * A: I _think_ it's OK. read_cache_page shouldn't deadlock, we'll write out the - * page OK. We'll actually write it out again in commit_write, which is a little - * suboptimal, but at least we're correct. - */ + /* The rules state that we must obtain the page lock *before* f->sem, so + * drop f->sem temporarily. Since we also hold c->alloc_sem, nothing's + * actually going to *change* so we're safe; we only allow reading. + * + * It is important to note that jffs2_write_begin() will ensure that its + * page is marked Uptodate before allocating space. That means that if we + * end up here trying to GC the *same* page that jffs2_write_begin() is + * trying to write out, read_cache_page() will not deadlock. */ + mutex_unlock(&f->sem); pg_ptr = jffs2_gc_fetch_page(c, f, start, &pg); + mutex_lock(&f->sem); if (IS_ERR(pg_ptr)) { printk(KERN_WARNING "read_cache_page() returned error: %ld\n", PTR_ERR(pg_ptr));