From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. Bruce Fields" Subject: [PATCH, RESEND] locks: fix possible infinite loop in posix deadlock detection Date: Tue, 30 Oct 2007 11:20:02 -0400 Message-ID: <20071030152002.GA21595@fieldses.org> References: <20071017185157.GC3785@mvista.com> <20071018185759.GU3785@mvista.com> <20071026170750.GC13033@fieldses.org> <20071026224707.GO13033@fieldses.org> <20071028173136.GA16905@fieldses.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, "George G. Davis" , Andrew Morton , linux-fsdevel@vger.kernel.org To: Linus Torvalds , stable@kernel.org Return-path: Received: from mail.fieldses.org ([66.93.2.214]:54467 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752560AbXJ3PUQ (ORCPT ); Tue, 30 Oct 2007 11:20:16 -0400 Content-Disposition: inline In-Reply-To: <20071028173136.GA16905@fieldses.org> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org From: J. Bruce Fields It's currently possible to send posix_locks_deadlock() into an infinite loop (under the BKL). For now, fix this just by bailing out after a few iterations. We may want to fix this in a way that better clarifies the semantics of deadlock detection. But that will take more time, and this minimal fix is probably adequate for any realistic scenario, and is simple enough to be appropriate for applying to stable kernels now. Thanks to George Davis for reporting the problem. Cc: "George G. Davis" Signed-off-by: J. Bruce Fields --- fs/locks.c | 11 +++++++++++ 1 files changed, 11 insertions(+), 0 deletions(-) I didn't see objections to this quick fix (just to the followup that attempts to rip out posix deadlock detection entirely), so I'm resending with just comment modifications. I haven't given up on a more comprehensive solution, but I think we really need to apply some fix now. --b. diff --git a/fs/locks.c b/fs/locks.c index 0127a28..8b8388e 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -696,17 +696,28 @@ EXPORT_SYMBOL(posix_test_lock); * Note: the above assumption may not be true when handling lock requests * from a broken NFS client. But broken NFS clients have a lot more to * worry about than proper deadlock detection anyway... --okir + * + * However, the failure of this assumption (also possible in the case of + * multiple tasks sharing the same open file table) also means there's no + * guarantee that the loop below will terminate. As a hack, we give up + * after a few iterations. */ + +#define MAX_DEADLK_ITERATIONS 10 + static int posix_locks_deadlock(struct file_lock *caller_fl, struct file_lock *block_fl) { struct file_lock *fl; + int i = 0; next_task: if (posix_same_owner(caller_fl, block_fl)) return 1; list_for_each_entry(fl, &blocked_list, fl_link) { if (posix_same_owner(fl, block_fl)) { + if (i++ > MAX_DEADLK_ITERATIONS) + return 0; fl = fl->fl_next; block_fl = fl; goto next_task; -- 1.5.3.4.208.gc990