Paul Menage e7c5ec9193 cgroups: add css_tryget()
Add css_tryget(), that obtains a counted reference on a CSS.  It is used
in situations where the caller has a "weak" reference to the CSS, i.e.
one that does not protect the cgroup from removal via a reference count,
but would instead be cleaned up by a destroy() callback.

css_tryget() will return true on success, or false if the cgroup is being
removed.

This is similar to Kamezawa Hiroyuki's patch from a week or two ago, but
with the difference that in the event of css_tryget() racing with a
cgroup_rmdir(), css_tryget() will only return false if the cgroup really
does get removed.

This implementation is done by biasing css->refcnt, so that a refcnt of 1
means "releasable" and 0 means "released or releasing".  In the event of a
race, css_tryget() distinguishes between "released" and "releasing" by
checking for the CSS_REMOVED flag in css->flags.

Signed-off-by: Paul Menage <menage@google.com>
Tested-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-01-08 08:31:10 -08:00
..
2009-01-04 12:17:42 +01:00
2009-01-07 17:38:32 -05:00
2008-11-11 21:15:50 -05:00
2008-10-20 11:01:52 -07:00
2008-12-29 08:29:50 +01:00
2008-12-03 22:12:38 -08:00
2008-12-03 22:12:38 -08:00
2008-10-20 08:52:42 -07:00
2009-01-06 15:59:29 -08:00
2009-01-01 10:12:19 +10:30
2008-12-29 08:29:50 +01:00
2008-11-26 12:13:34 +01:00
2009-01-04 13:33:20 -08:00
2008-11-12 17:17:18 -08:00
2009-01-08 08:31:10 -08:00
2008-10-16 11:21:32 -07:00
2008-11-30 11:00:15 -08:00
2009-01-02 12:19:34 -08:00
2008-12-29 17:47:23 +10:00
2008-12-25 11:01:43 +11:00
2008-11-24 18:57:41 -05:00
2008-12-31 18:07:38 -05:00
2008-12-29 07:39:34 -05:00
2008-10-16 16:53:13 +02:00
2008-12-15 23:44:31 -08:00
2008-12-29 11:27:46 +02:00
2008-12-31 18:07:42 -05:00
2008-12-01 19:14:02 +01:00
2009-01-06 15:59:01 -08:00
2008-10-16 11:21:40 -07:00
2008-12-08 01:14:16 -08:00
2009-01-07 14:29:17 +01:00
2008-10-16 11:21:38 -07:00
2008-12-31 18:07:42 -05:00
2008-10-29 22:02:09 +01:00
2008-11-03 18:21:45 +01:00
2008-10-15 14:24:08 +02:00
2009-01-05 08:40:30 -08:00
2009-01-08 08:31:00 -08:00
2009-01-05 08:40:30 -08:00
2008-12-31 15:11:46 +01:00
2009-01-03 14:11:07 +01:00
2008-10-20 22:34:12 +01:00
2008-12-28 22:43:21 -05:00
2009-01-06 15:58:58 -08:00
2009-01-08 08:31:07 -08:00
2008-11-06 15:41:21 -08:00
2008-12-08 14:31:59 +01:00
2008-11-19 18:49:57 -08:00
2009-01-04 16:13:40 -08:00
2009-01-07 17:38:31 -05:00
2008-12-23 15:21:45 -05:00
2008-12-19 15:22:54 -05:00
2008-12-21 14:21:14 +11:00
2009-01-08 08:31:05 -08:00
2008-10-16 11:21:49 -07:00
2008-11-28 16:24:56 -08:00
2008-12-04 09:09:37 +01:00
2008-11-07 22:56:00 -08:00
2008-11-20 04:10:00 -08:00
2009-01-06 10:44:30 -08:00
2008-10-23 00:11:07 -04:00
2009-01-06 15:59:12 -08:00
2008-10-23 18:54:05 +04:00
2008-12-20 09:15:46 +01:00
2009-01-05 18:31:12 -08:00
2008-11-12 17:17:17 -08:00
2008-11-16 19:39:21 -08:00
2009-01-04 13:33:20 -08:00
2009-01-07 09:58:22 +11:00
2008-12-15 23:42:33 -08:00
2008-12-30 09:05:16 +10:30
2008-11-24 21:27:22 -08:00
2008-11-02 10:15:07 -08:00
2009-01-08 08:31:10 -08:00
2008-10-16 11:21:47 -07:00
2009-01-01 10:12:25 +10:30
2008-12-12 17:01:38 +01:00
2009-01-02 10:19:36 -08:00
2009-01-07 10:00:14 -08:00
2008-10-16 11:21:31 -07:00
2009-01-06 15:59:09 -08:00