| Re: [PATCH v2 4/5] don't take cgroup_mutex in destroy() [message #46044 is a reply to message #46035] |
Tue, 24 April 2012 02:31   |
KAMEZAWA Hiroyuki
Messages: 463
Registered: September 2006
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Senior Member |
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(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@parallels.com>
> CC: Tejun Heo <tj@kernel.org>
> CC: Li Zefan <lizefan@huawei.com>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> CC: Vivek Goyal <vgoyal@redhat.com>
> ---
> 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 ?
Thanks,
-Kame
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