Hugh Dickins 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> Acked-by: Li Zefan <lizf@xxxxxxxxxxxxxx> > --- > > include/linux/cgroup.h | 2 +- > kernel/cgroup.c | 19 +++++++++---------- > lib/idr.c | 4 ++-- > 3 files changed, 12 insertions(+), 13 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
