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. _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "[email protected]"
