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: revert that commit, restoring
ss->id_lock to a spinlock.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Acked-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
---
include/linux/cgroup.h | 2 +-
kernel/cgroup.c | 18 +++++++++---------
2 files changed, 10 insertions(+), 10 deletions(-)
--- 3.2.0+.orig/include/linux/cgroup.h 2012-01-14 13:01:57.000000000 -0800
+++ 3.2.0+/include/linux/cgroup.h 2012-01-19 12:14:47.420233522 -0800
@@ -535,7 +535,7 @@ 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;
--- 3.2.0+.orig/kernel/cgroup.c 2012-01-14 13:01:57.000000000 -0800
+++ 3.2.0+/kernel/cgroup.c 2012-01-19 12:16:04.132235263 -0800
@@ -4939,9 +4939,9 @@ void free_css_id(struct cgroup_subsys *s
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);
@@ -4967,10 +4967,10 @@ static struct css_id *get_new_cssid(stru
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) {
@@ -4985,9 +4985,9 @@ static struct css_id *get_new_cssid(stru
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);
@@ -4999,7 +4999,7 @@ static int __init_or_module cgroup_init_
{
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);
@@ -5094,9 +5094,9 @@ css_get_next(struct cgroup_subsys *ss, i
* 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;
--
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