This is a note to let you know that I've just added the patch titled jffs2: Fix page lock / f->sem deadlock to the 3.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: jffs2-fix-page-lock-f-sem-deadlock.patch and it can be found in the queue-3.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 49e91e7079febe59a20ca885a87dd1c54240d0f1 Mon Sep 17 00:00:00 2001 From: David Woodhouse <David.Woodhouse@xxxxxxxxx> Date: Mon, 1 Feb 2016 12:37:20 +0000 Subject: jffs2: Fix page lock / f->sem deadlock MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: David Woodhouse <David.Woodhouse@xxxxxxxxx> commit 49e91e7079febe59a20ca885a87dd1c54240d0f1 upstream. With this fix, all code paths should now be obtaining the page lock before f->sem. Reported-by: Szabó Tamás <sztomi89@xxxxxxxxx> Tested-by: Thomas Betker <thomas.betker@xxxxxxxxxxxxxxxxx> Signed-off-by: David Woodhouse <David.Woodhouse@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -1296,14 +1296,17 @@ 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)) { pr_warn("read_cache_page() returned error: %ld\n", Patches currently in stable-queue which might be from David.Woodhouse@xxxxxxxxx are queue-3.14/revert-jffs2-fix-lock-acquisition-order-bug-in-jffs2_write_begin.patch queue-3.14/jffs2-fix-page-lock-f-sem-deadlock.patch queue-3.14/fix-directory-hardlinks-from-deleted-directories.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html