Now that we know that the forking task can't migrate amd the child is always moved to the same cgroup by cgroup_post_fork()->css_set_move_task() we can change pids_can_fork() and pids_cancel_fork() to just use task_css(current). And since we no longer need to pin this css, we can remove pid_fork().
Note: the patch uses task_css_check(true), perhaps it makes sense to add a helper or change task_css_set_check() to take cgroup_threadgroup_rwsem into account. Signed-off-by: Oleg Nesterov <[email protected]> --- kernel/cgroup_pids.c | 41 ++++++++++------------------------------- 1 files changed, 10 insertions(+), 31 deletions(-) diff --git a/kernel/cgroup_pids.c b/kernel/cgroup_pids.c index 15ef2e4..de3359a 100644 --- a/kernel/cgroup_pids.c +++ b/kernel/cgroup_pids.c @@ -205,48 +205,28 @@ static void pids_cancel_attach(struct cgroup_subsys_state *css, } } +/* + * task_css_check(true) in pids_can_fork() and pids_cancel_fork() relies + * on threadgroup_change_begin() held by the copy_process(). + */ static int pids_can_fork(struct task_struct *task, void **priv_p) { struct cgroup_subsys_state *css; struct pids_cgroup *pids; - int err; - /* - * Use the "current" task_css for the pids subsystem as the tentative - * css. It is possible we will charge the wrong hierarchy, in which - * case we will forcefully revert/reapply the charge on the right - * hierarchy after it is committed to the task proper. - */ - css = task_get_css(current, pids_cgrp_id); + css = task_css_check(current, pids_cgrp_id, true); pids = css_pids(css); - - err = pids_try_charge(pids, 1); - if (err) - goto err_css_put; - - *priv_p = css; - return 0; - -err_css_put: - css_put(css); - return err; + return pids_try_charge(pids, 1); } static void pids_cancel_fork(struct task_struct *task, void *priv) { - struct cgroup_subsys_state *css = priv; - struct pids_cgroup *pids = css_pids(css); + struct cgroup_subsys_state *css; + struct pids_cgroup *pids; + css = task_css_check(current, pids_cgrp_id, true); + pids = css_pids(css); pids_uncharge(pids, 1); - css_put(css); -} - -static void pids_fork(struct task_struct *task, void *priv) -{ - struct cgroup_subsys_state *css = priv; - - WARN_ON(task_css_check(task, pids_cgrp_id, true) != css); - css_put(css); } static void pids_free(struct task_struct *task) @@ -329,7 +309,6 @@ struct cgroup_subsys pids_cgrp_subsys = { .cancel_attach = pids_cancel_attach, .can_fork = pids_can_fork, .cancel_fork = pids_cancel_fork, - .fork = pids_fork, .free = pids_free, .legacy_cftypes = pids_files, .dfl_cftypes = pids_files, -- 1.5.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
