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Commit 42aee6c4 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

cgroup: revert ss_id_lock to spinlock 



Commit c1e2ee2d ("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: revert that commit, restoring ss->id_lock to a spinlock.

Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9f7de827

include/linux/cgroup.h

+1 −1
Original line number Diff line number Diff line
@@ -498,7 +498,7 @@ struct cgroup_subsys { 
	struct list_head sibling;

	/* used when use_id == true */

	struct idr idr;

	rwlock_t id_lock;

	spinlock_t id_lock;



	/* should be defined only by modular subsystems */

	struct module *module;

kernel/cgroup.c

+9 −9
Original line number Diff line number Diff line
@@ -4885,9 +4885,9 @@ void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css) 


	rcu_assign_pointer(id->css, NULL);

	rcu_assign_pointer(css->id, NULL);

	write_lock(&ss->id_lock);

	spin_lock(&ss->id_lock);

	idr_remove(&ss->idr, id->id);

	write_unlock(&ss->id_lock);

	spin_unlock(&ss->id_lock);

	kfree_rcu(id, rcu_head);

}

EXPORT_SYMBOL_GPL(free_css_id);
@@ -4913,10 +4913,10 @@ static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth) 
		error = -ENOMEM;

		goto err_out;

	}

	write_lock(&ss->id_lock);

	spin_lock(&ss->id_lock);

	/* Don't use 0. allocates an ID of 1-65535 */

	error = idr_get_new_above(&ss->idr, newid, 1, &myid);

	write_unlock(&ss->id_lock);

	spin_unlock(&ss->id_lock);



	/* Returns error when there are no free spaces for new ID.*/

	if (error) {
@@ -4931,9 +4931,9 @@ static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth) 
	return newid;

remove_idr:

	error = -ENOSPC;

	write_lock(&ss->id_lock);

	spin_lock(&ss->id_lock);

	idr_remove(&ss->idr, myid);

	write_unlock(&ss->id_lock);

	spin_unlock(&ss->id_lock);

err_out:

	kfree(newid);

	return ERR_PTR(error);
@@ -4945,7 +4945,7 @@ static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss, 
{

	struct css_id *newid;



	rwlock_init(&ss->id_lock);

	spin_lock_init(&ss->id_lock);

	idr_init(&ss->idr);



	newid = get_new_cssid(ss, 0);
@@ -5040,9 +5040,9 @@ css_get_next(struct cgroup_subsys *ss, int id, 
		 * scan next entry from bitmap(tree), tmpid is updated after

		 * idr_get_next().

		 */

		read_lock(&ss->id_lock);

		spin_lock(&ss->id_lock);

		tmp = idr_get_next(&ss->idr, &tmpid);

		read_unlock(&ss->id_lock);

		spin_unlock(&ss->id_lock);



		if (!tmp)

			break;