on 15/02/2014 22:02 Konstantin Belousov said the following:
> On Sat, Feb 15, 2014 at 02:12:40PM +0200, Andriy Gapon wrote:
>> on 14/02/2014 21:18 Jeremie Le Hen said the following:
>>> I've just got another occurence of the exact same panic.  Any clue how 
>>> to debug this?
>> Could you please obtain *vp from frame 12 ?
>> The problem seems to be happening in this piece of ZFS code: if
>> (cnp->cn_flags & ISDOTDOT) { ltype = VOP_ISLOCKED(dvp); VOP_UNLOCK(dvp,
>> 0); } ZFS_EXIT(zfsvfs); error = vn_lock(*vpp, cnp->cn_lkflags); if
>> (cnp->cn_flags & ISDOTDOT) vn_lock(dvp, ltype | LK_RETRY);
>> ltype is apparently LK_SHARED and the assertion is apparently triggered
>> by EDEADLK error.  The error can occur only if a thread tries to obtain a
>> lock in a shared mode when it already has the lock exclusively. My only
>> explanation of how this could happen is that dvp == *vpp and cn_lkflags 
>> is LK_EXCLUSIVE.  In other words, this is a dot-dot lookup that results
>> in the same vnode.  I think that this is only possible if dvp is the root
>> vnode. I am not sure if my theory is correct though. Also, I am not sure
>> if zfs_lookup() should be prepared to handle such a lookup or if this
>> kind of lookup should be handled by upper/other layers.  In this case 
>> these would be VFS lookup code and nullfs code.
> So, is VV_ROOT flag set on the corresponding ZFS vnode ?

As Jeremy has just reported, yes, it is set.

> Just in case, you could try the following change, but I doubt that it would
> have any effect.  Nullfs root vnode is cached so its VV_ROOT flag should
> not be lost.  Also, I never seen similar issue with UFS.

I have never seen this issue with ZFS... before.

> diff --git a/sys/fs/nullfs/null_subr.c b/sys/fs/nullfs/null_subr.c index
> fa6c4af..3f74579 100644 --- a/sys/fs/nullfs/null_subr.c +++
> b/sys/fs/nullfs/null_subr.c @@ -251,6 +251,7 @@ null_nodeget(mp, lowervp,
> vpp) vp->v_type = lowervp->v_type; vp->v_data = xp; vp->v_vnlock =
> lowervp->v_vnlock; +  vp->v_vflag = lowervp->v_vflag & VV_ROOT; error =
> insmntque1(vp, mp, null_insmntque_dtr, xp); if (error != 0) return
> (error);

Andriy Gapon
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