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cgroup: pids: fix race between cgroup_post_fork() and cgroup_migrate()

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If the new child migrates to another cgroup before cgroup_post_fork() calls
subsys->fork(), then both pids_can_attach() and pids_fork() will do the same
pids_uncharge(old_pids) + pids_charge(pids) sequence twice.

Change copy_process() to call threadgroup_change_begin/threadgroup_change_end
unconditionally. percpu_down_read() is cheap and this allows other cleanups,
see the next changes.

Also, this way we can unify cgroup_threadgroup_rwsem and dup_mmap_sem.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Zefan Li <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Oleg Nesterov 2015-11-27 19:57:19 +01:00 • committed by Tejun Heo
parent 53254f900b
commit c9e75f0492
2 changed files with 5 additions and 25 deletions
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21
kernel/cgroup_pids.c
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@ -243,27 +243,10 @@ static void pids_cancel_fork(struct task_struct *task, void *priv)
static void pids_fork(struct task_struct *task, void *priv)
{
struct cgroup_subsys_state *css;
struct cgroup_subsys_state *old_css = priv;
struct pids_cgroup *pids;
struct pids_cgroup *old_pids = css_pids(old_css);
css = task_get_css(task, pids_cgrp_id);
pids = css_pids(css);
/*
* If the association has changed, we have to revert and reapply the
* charge/uncharge on the wrong hierarchy to the current one. Since
* the association can only change due to an organisation event, its
* okay for us to ignore the limit in this case.
*/
if (pids != old_pids) {
pids_uncharge(old_pids, 1);
pids_charge(pids, 1);
}
struct cgroup_subsys_state *css = priv;
WARN_ON(task_css_check(task, pids_cgrp_id, true) != css);
css_put(css);
css_put(old_css);
}
static void pids_free(struct task_struct *task)