MFC r269708: Unlock ldvp and lock dvp to compensate for possible ldvp unlock in lower VOP_LOOKUP() and dvp reclamation.  Use cached value of dvp->v_mount.
MFC r269708:
Unlock ldvp and lock dvp to compensate for possible ldvp unlock in lower
VOP_LOOKUP() and dvp reclamation.  Use cached value of dvp->v_mount.

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