On Wed, 18 Jan 2012 22:05:12 -0800 (PST) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > Commit c1e2ee2dc436 "memcg: replace ss->id_lock with a rwlock" has > now been seen to cause the unfair behavior we should have expected > from converting a spinlock to an rwlock: softlockup in cgroup_mkdir(), > whose get_new_cssid() is waiting for the wlock, while there are 19 > tasks using the rlock in css_get_next() to get on with their memcg > workload (in an artificial test, admittedly). Yet lib/idr.c was > made suitable for RCU way back. > > 1. Revert that commit, restoring ss->id_lock to a spinlock. > > 2. Make one small adjustment to idr_get_next(): take the height from > the top layer (stable under RCU) instead of from the root (unprotected > by RCU), as idr_find() does. > > 3. Remove lock and unlock around css_get_next()'s call to idr_get_next(): > memcg iterators (only users of css_get_next) already did rcu_read_lock(), > and comment demands that, but add a WARN_ON_ONCE to make sure of it. > > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Thank you ! This seems much better. Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>