mm: don't hold css->refcnt during traversal

To obtain the pointer to the next memcg position, mem_cgroup_iter()
currently holds css->refcnt during memcg traversal only to put css->refcnt
at the end of the routine.  This isn't necessary as an rcu_read_lock is
already held throughout the function.  The use of the RCU read lock with
css_next_descendant_pre() guarantees that sibling linkage is safe without
holding a ref on the passed-in @css.

Remove css->refcnt usage during traversal by leveraging RCU.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kinsey Ho <[email protected]>
Reviewed-by: T.J. Mercier <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Michal Koutný <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Cc: Zefan Li <[email protected]>
Cc: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions