cgroup: replace tasklist_lock with rcu_read_lock

We can replace the tasklist_lock in cgroup_attach_proc with an
rcu_read_lock().

Changes in V4:
* https://lkml.org/lkml/2011/12/23/284 (Frederic Weisbecker)
  * Minimize size of rcu_read_lock critical section
  * Add comment
* https://lkml.org/lkml/2011/12/26/136 (Li Zefan)
  * Split into two patches
Changes in V3:
* https://lkml.org/lkml/2011/12/22/419 (Frederic Weisbecker)
  * Add an rcu_read_lock to protect against exit
Changes in V2:
* https://lkml.org/lkml/2011/12/22/86 (Tejun Heo)
  * Use a goto instead of returning -EAGAIN

Suggested-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Mandeep Singh Baines <[email protected]>
Acked-by: Li Zefan <[email protected]>
Acked-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Paul Menage <[email protected]>

0 files changed, 0 insertions, 0 deletions