On Thu 22-11-12 14:29:49, Glauber Costa wrote:
> With more than one user, it is useful to have a helper function in the
> cgroup core to derive a group's name.
>
> We'll just return a pointer, and it is not expected to get incredibly
> complicated. But it is useful to have it so we can abstract away the
> vfs relation from its users.
>
> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
> CC: Tejun Heo <tj@xxxxxxxxxx>
> CC: Michal Hocko <mhocko@xxxxxxx>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> CC: Johannes Weiner <hannes@xxxxxxxxxxx>
Looks good to me in general. Minor comments bellow.
Anyway.
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> Tejun:
>
> I know the rcu is no longer necessary. I am using mhocko's tree,
> that doesn't seem to have your last stream of patches yet.
Which patches are we talking about? Are they in a pullable (for -mm)
branch or I have to cherry-pick them?
> If you approve the interface, we'll need a follow up on this to remove
> the rcu dereference of the dentry.
>
> include/linux/cgroup.h | 1 +
> kernel/cgroup.c | 9 +++++++++
> mm/memcontrol.c | 11 ++++-------
> 3 files changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index a178a91..57c4ab1 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -401,6 +401,7 @@ int cgroup_rm_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts);
> int cgroup_is_removed(const struct cgroup *cgrp);
>
> int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
> +extern const char *cgroup_name(const struct cgroup *cgrp);
>
> int cgroup_task_count(const struct cgroup *cgrp);
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 3d68aad..d0d291e 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1757,6 +1757,15 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
> }
> EXPORT_SYMBOL_GPL(cgroup_path);
>
This expects css reference at caller, right. Please make it explicit
here in case somebody wants to use this somewhere else.
Besides that rcu_read_{un}lock are not necessary if you keep the
reference, right? The last dput happens only after the last css_put.
> +const char *cgroup_name(const struct cgroup *cgrp)
> +{
> + struct dentry *dentry;
> + rcu_read_lock();
> + dentry = rcu_dereference_check(cgrp->dentry, cgroup_lock_is_held());
> + rcu_read_unlock();
> + return dentry->d_name.name;
> +}
> +
> /*
> * Control Group taskset
> */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e3d805f..05b87aa 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3141,16 +3141,13 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
> static char *memcg_cache_name(struct mem_cgroup *memcg, struct kmem_cache *s)
> {
> char *name;
> - struct dentry *dentry;
> + const char *cgname;
>
> - rcu_read_lock();
> - dentry = rcu_dereference(memcg->css.cgroup->dentry);
> - rcu_read_unlock();
> -
> - BUG_ON(dentry == NULL);
> + cgname = cgroup_name(memcg->css.cgroup);
> + BUG_ON(cgname == NULL);
>
> name = kasprintf(GFP_KERNEL, "%s(%d:%s)", s->name,
> - memcg_cache_id(memcg), dentry->d_name.name);
> + memcg_cache_id(memcg), cgname);
>
> return name;
> }
> --
> 1.7.11.7
>
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--
Michal Hocko
SUSE Labs
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