kref: Implement kref_get_unless_zero v3
authorThomas Hellstrom <thellstrom@vmware.com>
Tue, 6 Nov 2012 11:31:49 +0000 (11:31 +0000)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 17 Apr 2013 04:27:26 +0000 (21:27 -0700)
commite3a55052f4773105dbd23f72dec4aeac82dea871
tree287ba056309faab0f819fa03b74f6770430d5b49
parent7077c66b3ab3a1d336648cf88f54df43709ebac3
kref: Implement kref_get_unless_zero v3

commit 4b20db3de8dab005b07c74161cb041db8c5ff3a7 upstream.

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.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
include/linux/kref.h