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| author | Thomas Hellstrom <thellstrom@vmware.com> | 2012-11-06 11:31:49 +0000 |
|---|---|---|
| committer | Dave Airlie <airlied@redhat.com> | 2012-11-20 16:15:02 +1000 |
| commit | 4b20db3de8dab005b07c74161cb041db8c5ff3a7 (patch) | |
| tree | 894e7d485b2e5d2b1ae0652b55dcd0f3f249fe8b /include/linux/kref.h | |
| parent | d7144556195ab04a148e722a93103da5438bdf78 (diff) | |
| download | lwn-4b20db3de8dab005b07c74161cb041db8c5ff3a7.tar.gz lwn-4b20db3de8dab005b07c74161cb041db8c5ff3a7.zip | |
kref: Implement kref_get_unless_zero v3
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>
Diffstat (limited to 'include/linux/kref.h')
| -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 65af6887872f..4972e6e9ca93 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -111,4 +111,25 @@ static inline int kref_put_mutex(struct kref *kref, } return 0; } + +/** + * 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_ */ |