Re: 5.99.42/i386 crash (backtrace + core available)

[Adam Hamsik <haaaad%gmail.com@localhost>]

On Jan,Sunday 9 2011, at 5:48 PM, Juergen Hannken-Illjes wrote:

> On Sat, Jan 08, 2011 at 11:16:19PM +0000, David Holland wrote:
>> On Tue, Dec 28, 2010 at 05:37:43PM +0100, Dennis den Brok wrote:
>>> rw_abort()
>>> rw_vector_enter(df829668, ...)
>>                   ^^^^^^^^
>>> genfs_lock()
>>> layer_bypass()
>>> VOP_LOCK(e15c2170,2)
>>            ^^^^^^^^
>>> vclean()
>>> getcleanvnode()
>>> getnewvnode()
>>> ffs_vget()
>>> ufs_lookup()
>>> VOP_LOOKUP(df8295c8,...)
>>              ^^^^^^^^
>> 
>> Unfortunately most of the things visible in the stack trace are vnode
>> op argument structures and not pointers to anything interesting.
>> However, since rw_vector_enter is passed &vp->v_lock, I think we can
>> tentatively conclude that it's trying to lock the same vnode that was
>> passed to VOP_LOOKUP, and it's failing because that's quite properly
>> already locked.
>> 
>> It looks like what happened is that ffs went to get a fresh vnode and
>> got a not-recently-used nullfs vnode. However, the nullfs vnode turned
>> out to be the nullfs vnode sitting on top of the ffs vnode it was
>> already working with. Since these share locks now, the vnode was
>> locked even though not recently used (and on the list to be cleaned
>> and all that), and in fact it turned out to be the same ffs vnode this
>> process was already working on, so trying to lock it for cleaning blew
>> up.
>> 
>> So this seems like fallout from Juergen's layer locking cleanup from a
>> few months ago. Not sure what the proper solution is, though.
> 
> Looks like we have
> 
>       vnode e15c2170, type nullfs with lower vnode df8295c8, type ffs
> 
> so here we lookup the lower vnode, need a new one and hit the upper (nullfs)
> vnode.  Trying to lock it always has to lock the lower vnode.  This is the
> background of ad's comment in vclean
> 
>       /* XXXAD should not lock vnode under layer */
>       mutex_exit(&vp->v_interlock);
>       VOP_LOCK(vp, LK_EXCLUSIVE);

Move locking to fs level from vnode level :) *shrugs*

Regards

Adam.