Re: [RFC][PATCH] nfsd: add +1 to reference counting scheme for struct nfsd4_session

On Mon, Feb 13, 2017 at 5:38 AM, Christoph Hellwig [off-list ref] wrote:

On Sat, Feb 11, 2017 at 09:01:15AM -0500, David Windsor wrote:

quoted

I'm not sure there's another way to accomplish what we need
(initializing struct nfsd4_session objects with refcount=1) without
also modifying the freeable reference state.  After migrating to the
refcount_t API, if we leave init_session() as is, the first call to
nfsd4_get_session_locked() will fail:

Which is a pretty clear indicator that this code should simply not
migrate to the recount_t API.  Why was it even considered if the
conversion is obviously broken?

I'm not sure this is a sound argument for not converting to
refcount_t.  In other locations in which refcounting schemes are
"unnatural," i.e. freeing refcounted objects when their refcount is -1
(rather than 0), conversion to refcount_t is accomplished by
performing a logical +1 to the overall refcounting scheme.  We're
auditing all refcounting corner cases, such as these, to see if
similar solutions can be found.

Thanks,
David
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