From owner-freebsd-fs@FreeBSD.ORG Wed Sep 24 13:32:48 2014 Return-Path: Delivered-To: freebsd-fs@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id C9F77B76 for ; Wed, 24 Sep 2014 13:32:48 +0000 (UTC) Received: from relay01.pair.com (relay01.pair.com [209.68.5.15]) by mx1.freebsd.org (Postfix) with SMTP id 7E84BC64 for ; Wed, 24 Sep 2014 13:32:47 +0000 (UTC) Received: (qmail 69732 invoked from network); 24 Sep 2014 13:26:07 -0000 Received: from 87.58.146.155 (HELO x2.osted.lan) (87.58.146.155) by relay01.pair.com with SMTP; 24 Sep 2014 13:26:07 -0000 X-pair-Authenticated: 87.58.146.155 Received: from x2.osted.lan (localhost [127.0.0.1]) by x2.osted.lan (8.14.5/8.14.5) with ESMTP id s8ODQ649012026; Wed, 24 Sep 2014 15:26:06 +0200 (CEST) (envelope-from pho@x2.osted.lan) Received: (from pho@localhost) by x2.osted.lan (8.14.5/8.14.5/Submit) id s8ODQ6T9012025; Wed, 24 Sep 2014 15:26:06 +0200 (CEST) (envelope-from pho) Date: Wed, 24 Sep 2014 15:26:05 +0200 From: Peter Holm To: Konstantin Belousov Subject: Re: Deadlock with umount -f involving tmpfs on top of ZFS on r271170 Message-ID: <20140924132605.GA11772@x2.osted.lan> References: <5420D5FC.4030600@FreeBSD.org> <20140923131244.GC8870@kib.kiev.ua> <5422240F.4080003@FreeBSD.org> <20140924102758.GH8870@kib.kiev.ua> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140924102758.GH8870@kib.kiev.ua> User-Agent: Mutt/1.5.21 (2010-09-15) Cc: FreeBSD FS X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 24 Sep 2014 13:32:48 -0000 On Wed, Sep 24, 2014 at 01:27:58PM +0300, Konstantin Belousov wrote: > On Tue, Sep 23, 2014 at 08:53:19PM -0500, Bryan Drewery wrote: > > I tried your patch and still ran into the deadlock. Here is the debug > > information: https://people.freebsd.org/~bdrewery/vfs_deadlock.2.txt > > I see what is going on. Previous patch cannot help there. > > The problem is that kern_linkat() starts write with vn_start_write(9), > and then tries to execute namei(9) with a path potentially crossing > the mount point. If the mount point is being unmounted, unmount cannot > lay suspension on the filesystem due to writer, but it owns the covered > vnode lock. On the other hand, namei(9) is unable to cross the mount > point since covered vnode is locked, thus writer does not make progress. > > The similar issue exists in rename code. The deadlock is only possible > for filesystems which suspend writes on unmount; such fs are UFS and tmpfs. > > Try this. > > diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c > index b3b7ed5..9775480 100644 I had been trying different scenarios without much luck, but with your description I got the problem instantly. :) The patch is an improvement, but: http://people.freebsd.org/~pho/stress/log/kostik718.txt - Peter