panic: LK_RETRY set with incompatible flags (0x200400) or an error occured (11)

[Jeremie Le Hen]

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 ?

Sure:

$1 = {v_tag = 0xffffffff815019a5 "zfs", v_op = 0xffffffff815164a0, 
  v_data = 0xfffff80010dcb2e0, v_mount = 0xfffff80010dcd660, 
  v_nmntvnodes = {tqe_next = 0xfffff80010dc7ce8, 
    tqe_prev = 0xfffff80010dcd6c0}, v_un = {vu_mount = 0x0, 
    vu_socket = 0x0, vu_cdev = 0x0, vu_fifoinfo = 0x0}, 
  v_hashlist = {le_next = 0x0, le_prev = 0x0}, v_cache_src = {
    lh_first = 0xfffff8005aeefcb0}, v_cache_dst = {tqh_first = 0x0, 
    tqh_last = 0xfffff80010dc8050}, v_cache_dd = 0x0, v_lock = {
    lock_object = {lo_name = 0xffffffff815019a5 "zfs", 
      lo_flags = 117112832, lo_data = 0, lo_witness = 0x0}, 
    lk_lock = 18446735277920538624, lk_exslpfail = 0, lk_timo = 51, 
    lk_pri = 96}, v_interlock = {lock_object = {
      lo_name = 0xffffffff80b46085 "vnode interlock", 
      lo_flags = 16973824, lo_data = 0, lo_witness = 0x0}, 
    mtx_lock = 4}, v_vnlock = 0xfffff80010dc8068, v_actfreelist = {
    tqe_next = 0x0, tqe_prev = 0xfffff80010dc7da8}, v_bufobj = {
    bo_lock = {lock_object = {
        lo_name = 0xffffffff80b4e613 "bufobj interlock", 
        lo_flags = 86179840, lo_data = 0, lo_witness = 0x0}, 
      rw_lock = 1}, bo_ops = 0xffffffff80e2d440, 
    bo_object = 0xfffff800a30bbd00, bo_synclist = {le_next = 0x0, 
      le_prev = 0x0}, bo_private = 0xfffff80010dc8000, 
    __bo_vnode = 0xfffff80010dc8000, bo_clean = {bv_hd = {
        tqh_first = 0x0, tqh_last = 0xfffff80010dc8120}, bv_root = {
        pt_root = 0}, bv_cnt = 0}, bo_dirty = {bv_hd = {
        tqh_first = 0x0, tqh_last = 0xfffff80010dc8140}, bv_root = {
        pt_root = 0}, bv_cnt = 0}, bo_numoutput = 0, bo_flag = 0, 
    bo_bsize = 131072}, v_pollinfo = 0x0, v_label = 0x0, 
  v_lockf = 0x0, v_rl = {rl_waiters = {tqh_first = 0x0, 
      tqh_last = 0xfffff80010dc8188}, rl_currdep = 0x0}, 
  v_cstart = 0, v_lasta = 0, v_lastw = 0, v_clen = 0, v_holdcnt = 7, 
  v_usecount = 6, v_iflag = 512, v_vflag = 1, v_writecount = 0, 
  v_hash = 3, v_type = VDIR}


> 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.

-- 
Jeremie Le Hen

Scientists say the world is made up of Protons, Neutrons and Electrons.
They forgot to mention Morons.