Date: Fri, 12 Aug 2016 15:39:50 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Rick Macklem <rmacklem@uoguelph.ca> Cc: Harry Schmalzbauer <freebsd@omnilan.de>, Mark Johnston <markj@freebsd.org>, FreeBSD Stable <freebsd-stable@freebsd.org>, "kib@FreeBSD.org" <kib@FreeBSD.org> Subject: Re: unionfs bugs, a partial patch and some comments [Was: Re: 1-BETA3 Panic: __lockmgr_args: downgrade a recursed lockmgr nfs @ /usr/local/share/deploy-tools/RELENG_11/src/sys/fs/unionfs/union_vnops.c:1905] Message-ID: <20160812123950.GO83214@kib.kiev.ua> In-Reply-To: <YTOPR01MB0412B2A08F1A3C1A3B2EB160DD1E0@YTOPR01MB0412.CANPRD01.PROD.OUTLOOK.COM> References: <57A79E24.8000100@omnilan.de> <YQBPR01MB0401201977AEA8A803F27B23DD1A0@YQBPR01MB0401.CANPRD01.PROD.OUTLOOK.COM> <57A83C78.1070403@omnilan.de> <20160809060213.GA67664@raichu> <57A9A6C0.9060609@omnilan.de> <YTOPR01MB0412B2A08F1A3C1A3B2EB160DD1E0@YTOPR01MB0412.CANPRD01.PROD.OUTLOOK.COM>
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On Thu, Aug 11, 2016 at 10:53:03PM +0000, Rick Macklem wrote: > Harry Schmalzbauer wrote: > Bez??glich Mark Johnston's Nachricht vom 09.08.2016 08:02 (localtime): > ??? > >> > >> Just for anybody else needing unionfs: > >> https://people.freebsd.org/~attilio/unionfs_missing_insmntque_lock.patch > >> > >> This patch still applies and I'm successfully using this (unmodified) up > >> to FreeBSD-10.3 and never had any panic in all these years. > > > > Having spent some time looking at unionfs, I'm a bit skeptical that this > > patch will address the panic you reported earlier, though I'd be > > interested to know if it does. > [stuff snipped for brevity] > I took a look at this. (I know nothing about unionfs, but a little w.r.t. the VFS). > I can confirm that this function (unionfs_nodeget()) is weird and appears to > be broken to me. > > The function calls insmntque() before it initializes the vnode, which seems > racey, especially if it isn't LK_EXCLUSIVE locked. > Also, line#s 278-281: > if (uppervp != NULLVP) > vp->v_vnlock = uppervp->v_vnlock; > else > vp->v_vnlock = lowervp->v_vnlock; > so your patch isn't locking the vnode lock that it actually uses. > I think the vp argument to insmntque() is required to be LK_EXCLUSIVE > locked mostly so other threads won't fiddle with the vnode until this > function is done with it, but I am not sure? > > I think a more correct version of this (not saying it would be correct[????], > would call insmntque() later in the function, after it has been initialized. > (This means that the cleanup if it fails is more involved, but...) Yes. > > I've attached a patch (untested) that does this. Maybe you could try it? > > rick > ps: I've cc'd Kostik, in case he has some insight w.r.t. how this should be handled? > insmnque() performs the cleanup on its own, and that default cleanup is not suitable for the situation. I think that insmntque1() would better fit your requirements, your need to move the common code into a helper. It seems that unionfs_ins_cached_vnode() cleanup could reuse it.
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