On 04/23/2012 11:31 PM, KAMEZAWA Hiroyuki wrote:
> (2012/04/24 4:37), Glauber Costa wrote:
>
>> Most of the destroy functions are only doing very simple things
>> like freeing memory.
>>
>> The ones who goes through lists and such, already use its own
>> locking for those.
>>
>> * The cgroup itself won't go away until we free it, (after destroy)
>> * The parent won't go away because we hold a reference count
>> * There are no more tasks in the cgroup, and the cgroup is declared
>> dead (cgroup_is_removed() == true)
>>
>> [v2: don't cgroup_lock the freezer and blkcg ]
>>
>> Signed-off-by: Glauber Costa<glommer@xxxxxxxxxxxxx>
>> CC: Tejun Heo<tj@xxxxxxxxxx>
>> CC: Li Zefan<lizefan@xxxxxxxxxx>
>> CC: Kamezawa Hiroyuki<kamezawa.hiroyu@xxxxxxxxxxxxxx>
>> CC: Vivek Goyal<vgoyal@xxxxxxxxxx>
>> ---
>> kernel/cgroup.c | 9 ++++-----
>> 1 files changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>> index 932c318..976d332 100644
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>> @@ -869,13 +869,13 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
>> * agent */
>> synchronize_rcu();
>>
>> - mutex_lock(&cgroup_mutex);
>> /*
>> * Release the subsystem state objects.
>> */
>> for_each_subsys(cgrp->root, ss)
>> ss->destroy(cgrp);
>>
>> + mutex_lock(&cgroup_mutex);
>> cgrp->root->number_of_cgroups--;
>> mutex_unlock(&cgroup_mutex);
>>
>> @@ -3994,13 +3994,12 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
>>
>> err_destroy:
>>
>> + mutex_unlock(&cgroup_mutex);
>> for_each_subsys(root, ss) {
>> if (cgrp->subsys[ss->subsys_id])
>> ss->destroy(cgrp);
>> }
>>
>> - mutex_unlock(&cgroup_mutex);
>> -
>> /* Release the reference count that we took on the superblock */
>> deactivate_super(sb);
>>
>> @@ -4349,9 +4348,9 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
>> int ret = cgroup_init_idr(ss, css);
>> if (ret) {
>> dummytop->subsys[ss->subsys_id] = NULL;
>> + mutex_unlock(&cgroup_mutex);
>> ss->destroy(dummytop);
>> subsys[i] = NULL;
>> - mutex_unlock(&cgroup_mutex);
>> return ret;
>> }
>> }
>> @@ -4447,10 +4446,10 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
>> * pointer to find their state. note that this also takes care of
>> * freeing the css_id.
>> */
>> + mutex_unlock(&cgroup_mutex);
>> ss->destroy(dummytop);
>> dummytop->subsys[ss->subsys_id] = NULL;
>>
>
> I'm not fully sure but...dummytop->subsys[] update can be done without locking ?
>
I don't see a reason why updates to subsys[] after destruction shouldn't
be safe. But maybe I am wrong.
Tejun? Li?
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