From: Brian Behlendorf <behlendorf1@llnl.gov>
Subject: [PATCH] fix dnode constructor

The patch removes the extra call to dnode_cons() in dnode_create().  The
extra call to the constructor was there to reinitialize the non-trivial
data structures in the dnode (lists, mutexs, condvars, avl tree, etc).
This was safe, although not exactly clean, on Solaris because none of
the primitives allocate memory.  In the Linux port this is not true.
To keep stack usage to a minimum several of the primatives dynamically
allocate memory thus initializing them twice results in a memory leak.

This patch resolves this problem for Solaris and Linux by ensures all
*_init's are called in the constructor, and all *_destroy's are called
in the destructor.  Additionally we ensure that all dnode objects are
properly deconstructed before being freed to the slab, and when the
objects are allocated from the slab all required data members are
explicity initialized to correct values.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

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