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| author | Tejun Heo <tj@kernel.org> | 2014-11-18 08:49:52 +0100 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2014-11-18 08:49:52 +0100 |
| commit | eeecbd1971517103e06f11750dd1a9a1dc37e4e6 (patch) | |
| tree | ace58390ca7f2e7f7530a8a8b23d9449a00ae3be /kernel | |
| parent | cgroup: add cgroup_subsys->css_e_css_changed() (diff) | |
| download | linux-eeecbd1971517103e06f11750dd1a9a1dc37e4e6.tar.xz linux-eeecbd1971517103e06f11750dd1a9a1dc37e4e6.zip | |
cgroup: implement cgroup_get_e_css()
Implement cgroup_get_e_css() which finds and gets the effective css
for the specified cgroup and subsystem combination. This function
always returns a valid pinned css. This will be used by cgroup
writeback support.
While at it, add comment to cgroup_e_css() to explain why that
function is different from cgroup_get_e_css() and has to test
cgrp->child_subsys_mask instead of cgroup_css(cgrp, ss).
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/cgroup.c | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 69f033582a1a..bb263d0caab3 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -277,6 +277,10 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp, if (!(cgrp->root->subsys_mask & (1 << ss->id))) return NULL; + /* + * This function is used while updating css associations and thus + * can't test the csses directly. Use ->child_subsys_mask. + */ while (cgroup_parent(cgrp) && !(cgroup_parent(cgrp)->child_subsys_mask & (1 << ss->id))) cgrp = cgroup_parent(cgrp); @@ -284,6 +288,39 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp, return cgroup_css(cgrp, ss); } +/** + * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem + * @cgrp: the cgroup of interest + * @ss: the subsystem of interest + * + * Find and get the effective css of @cgrp for @ss. The effective css is + * defined as the matching css of the nearest ancestor including self which + * has @ss enabled. If @ss is not mounted on the hierarchy @cgrp is on, + * the root css is returned, so this function always returns a valid css. + * The returned css must be put using css_put(). + */ +struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp, + struct cgroup_subsys *ss) +{ + struct cgroup_subsys_state *css; + + rcu_read_lock(); + + do { + css = cgroup_css(cgrp, ss); + + if (css && css_tryget_online(css)) + goto out_unlock; + cgrp = cgroup_parent(cgrp); + } while (cgrp); + + css = init_css_set.subsys[ss->id]; + css_get(css); +out_unlock: + rcu_read_unlock(); + return css; +} + /* convenient tests for these bits */ static inline bool cgroup_is_dead(const struct cgroup *cgrp) { |