This function is intended to simplify locking around refcounting for objects that can be looked up from a lookup structure, and which are removed from that lookup structure in the object destructor. Operations on such objects require at least a read lock around lookup + kref_get, and a write lock around kref_put + remove from lookup structure. Furthermore, RCU implementations become extremely tricky. With a lookup followed by a kref_get_unless_zero *with return value check* locking in the kref_put path can be deferred to the actual removal from the lookup structure and RCU lookups become trivial. v2: Formatting fixes. v3: Invert the return value. Change-Id: Ibcb524294c2cebe1d832e77714895822adc1c89a Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com> Signed-off-by: Dave Airlie <airlied@redhat.com> Git-commit: 4b20db3de8dab005b07c74161cb041db8c5ff3a7 Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git [shrenujb@codeaurora.org: resolve trivial merge conflicts] Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>