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    Subject[PATCH 07/16] cgroup: factor out cgroup_apply_control_disable() from cgroup_subtree_control_write()
    Date
    Factor out css disabling and hiding into cgroup_apply_control_disable().

    * Nest subsystem walk inside child walk. The child walk will later be
    converted to subtree walk which is a bit more expensive.

    * Instead of operating on the differential masks @css_enable and
    @css_disable, simply disable or hide csses according to the current
    cgroup_control() and cgroup_ss_mask(). This leads to the same
    result and is simpler and more robust.

    * This allows error handling path to share the same code.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    ---
    kernel/cgroup.c | 74 ++++++++++++++++++++++++++++++++-------------------------
    1 file changed, 41 insertions(+), 33 deletions(-)

    diff --git a/kernel/cgroup.c b/kernel/cgroup.c
    index 7f1c636..4b8a6eb 100644
    --- a/kernel/cgroup.c
    +++ b/kernel/cgroup.c
    @@ -3011,6 +3011,43 @@ static bool cgroup_drain_offline(struct cgroup *cgrp)
    return false;
    }

    +/**
    + * cgroup_apply_control_disable - kill or hide csses according to control
    + * @cgrp: parent of the target cgroups
    + *
    + * Walk @cgrp's children and kill and hide csses so that they match
    + * cgroup_ss_mask() and cgroup_visible_mask().
    + *
    + * A css is hidden when the userland requests it to be disabled while other
    + * subsystems are still depending on it. The css must not actively control
    + * resources and be in the vanilla state if it's made visible again later.
    + * Controllers which may be depended upon should provide ->css_reset() for
    + * this purpose.
    + */
    +static void cgroup_apply_control_disable(struct cgroup *cgrp)
    +{
    + struct cgroup *dsct;
    + struct cgroup_subsys *ss;
    + int ssid;
    +
    + cgroup_for_each_live_child(dsct, cgrp) {
    + for_each_subsys(ss, ssid) {
    + struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
    +
    + if (!css)
    + continue;
    +
    + if (!(cgroup_ss_mask(dsct) & (1 << ss->id))) {
    + kill_css(css);
    + } else if (!(cgroup_control(dsct) & (1 << ss->id))) {
    + css_clear_dir(css, NULL);
    + if (ss->css_reset)
    + ss->css_reset(css);
    + }
    + }
    + }
    +}
    +
    /* change the enabled child controllers for a cgroup in the default hierarchy */
    static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
    char *buf, size_t nbytes,
    @@ -3159,27 +3196,8 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
    if (ret)
    goto err_undo_css;

    - /*
    - * All tasks are migrated out of disabled csses. Kill or hide
    - * them. A css is hidden when the userland requests it to be
    - * disabled while other subsystems are still depending on it. The
    - * css must not actively control resources and be in the vanilla
    - * state if it's made visible again later. Controllers which may
    - * be depended upon should provide ->css_reset() for this purpose.
    - */
    - do_each_subsys_mask(ss, ssid, disable) {
    - cgroup_for_each_live_child(child, cgrp) {
    - struct cgroup_subsys_state *css = cgroup_css(child, ss);
    -
    - if (css_disable & (1 << ssid)) {
    - kill_css(css);
    - } else {
    - css_clear_dir(css, NULL);
    - if (ss->css_reset)
    - ss->css_reset(css);
    - }
    - }
    - } while_each_subsys_mask();
    + /* all tasks are migrated out of disabled csses, commit disable */
    + cgroup_apply_control_disable(cgrp);

    kernfs_activate(cgrp->kn);
    ret = 0;
    @@ -3188,22 +3206,12 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
    return ret ?: nbytes;

    err_undo_css:
    + /* restore masks and shoot down new csses */
    cgrp->subtree_control = old_sc;
    cgrp->subtree_ss_mask = old_ss;

    - do_each_subsys_mask(ss, ssid, enable) {
    - cgroup_for_each_live_child(child, cgrp) {
    - struct cgroup_subsys_state *css = cgroup_css(child, ss);
    -
    - if (!css)
    - continue;
    + cgroup_apply_control_disable(cgrp);

    - if (css_enable & (1 << ssid))
    - kill_css(css);
    - else
    - css_clear_dir(css, NULL);
    - }
    - } while_each_subsys_mask();
    goto out_unlock;
    }

    --
    2.5.0
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