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cgroup: revert ss_id_lock to spinlock 

Commit c1e2ee2dc4 ("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: Hugh Dickins <hughd@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2012-03-21 16:34:21 -07:00 committed by Linus Torvalds
parent 9f7de8275b
commit 42aee6c495
2 changed files with 10 additions and 10 deletions
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2
include/linux/cgroup.h
View File

@ -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;

18
kernel/cgroup.c
View File

@ -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;