Messages in this thread Patch in this message | | | Date | Wed, 7 Nov 2012 09:15:08 -0800 | From | Tejun Heo <> | Subject | [PATCH 1/9 v2] cgroup: add cgroup_subsys->post_create() |
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Currently, there's no way for a controller to find out whether a new cgroup finished all ->create() allocatinos successfully and is considered "live" by cgroup.
This becomes a problem later when we add generic descendants walking to cgroup which can be used by controllers as controllers don't have a synchronization point where it can synchronize against new cgroups appearing in such walks.
This patch adds ->post_create(). It's called after all ->create() succeeded and the cgroup is linked into the generic cgroup hierarchy. This plays the counterpart of ->pre_destroy().
When used in combination with the to-be-added generic descendant iterators, ->post_create() can be used to implement reliable state inheritance. It will be explained with the descendant iterators.
v2: Added a paragraph about its future use w/ descendant iterators per Michal.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Michal Hocko <mhocko@suse.cz> Cc: Glauber Costa <glommer@parallels.com> --- If you can explain it better, please be my guest.
Thanks.
include/linux/cgroup.h | 1 + kernel/cgroup.c | 12 ++++++++++-- 2 files changed, 11 insertions(+), 2 deletions(-)
--- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -438,6 +438,7 @@ int cgroup_taskset_size(struct cgroup_ta struct cgroup_subsys { struct cgroup_subsys_state *(*create)(struct cgroup *cgrp); + void (*post_create)(struct cgroup *cgrp); void (*pre_destroy)(struct cgroup *cgrp); void (*destroy)(struct cgroup *cgrp); int (*can_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset); --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4060,10 +4060,15 @@ static long cgroup_create(struct cgroup if (err < 0) goto err_remove; - /* each css holds a ref to the cgroup's dentry */ - for_each_subsys(root, ss) + for_each_subsys(root, ss) { + /* each css holds a ref to the cgroup's dentry */ dget(dentry); + /* creation succeeded, notify subsystems */ + if (ss->post_create) + ss->post_create(cgrp); + } + /* The cgroup directory was pre-locked for us */ BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex)); @@ -4281,6 +4286,9 @@ static void __init cgroup_init_subsys(st ss->active = 1; + if (ss->post_create) + ss->post_create(&ss->root->top_cgroup); + /* this function shouldn't be used with modular subsystems, since they * need to register a subsys_id, among other things */ BUG_ON(ss->module);
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