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| author | Thomas Hellstrom <thellstrom@vmware.com> | 2012-11-06 11:31:49 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-04-16 21:27:26 -0700 |
| commit | e3a55052f4773105dbd23f72dec4aeac82dea871 (patch) | |
| tree | 287ba056309faab0f819fa03b74f6770430d5b49 /include | |
| parent | 7077c66b3ab3a1d336648cf88f54df43709ebac3 (diff) | |
| download | lwn-e3a55052f4773105dbd23f72dec4aeac82dea871.tar.gz lwn-e3a55052f4773105dbd23f72dec4aeac82dea871.zip | |
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>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/kref.h | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/include/linux/kref.h b/include/linux/kref.h index 9c07dcebded7..fd2a6162ad3d 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -93,4 +93,25 @@ static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref) { return kref_sub(kref, 1, release); } + +/** + * kref_get_unless_zero - Increment refcount for object unless it is zero. + * @kref: object. + * + * Return non-zero if the increment succeeded. Otherwise return 0. + * + * 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. + */ +static inline int __must_check kref_get_unless_zero(struct kref *kref) +{ + return atomic_add_unless(&kref->refcount, 1, 0); +} #endif /* _KREF_H_ */ |