From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. Bruce Fields" Subject: [PATCH] locks: fix possible infinite loop in posix deadlock detection Date: Sun, 28 Oct 2007 13:31:37 -0400 Message-ID: <20071028173136.GA16905@fieldses.org> References: <20071017185157.GC3785@mvista.com> <20071018185759.GU3785@mvista.com> <20071026170750.GC13033@fieldses.org> <20071026224707.GO13033@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]:34172 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752209AbXJ1Rbt (ORCPT ); Sun, 28 Oct 2007 13:31:49 -0400 Content-Disposition: inline In-Reply-To: <20071026224707.GO13033@fieldses.org> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org From: J. Bruce Fields I think the real solution is to remove deadlock detection completely; it's hard to imaagine applications really depend on it anyway. For now, though, just bail out after a few iterations. Thanks to George Davis for reporting the problem. Cc: "George G. Davis" Signed-off-by: J. Bruce Fields --- fs/locks.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index 0127a28..131aa88 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -696,17 +696,29 @@ 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. We don't bother returning EDEADLK in that case; + * the deadlock has probably already happened anyway. */ + +#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