github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-06-09 23:23:53 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

kref: Implement kref_get_unless_zero v3

Browse Source 
commit 4b20db3de8 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>
This commit is contained in:
Thomas Hellstrom 2012-11-06 11:31:49 +00:00 committed by Greg Kroah-Hartman
parent 7077c66b3a
commit e3a55052f4
1 changed files with 21 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
include/linux/kref.h
View File

@ -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_ */