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cgroup: update cgroup_enable_task_cg_lists() to grab siglock
Currently, there's nothing preventing cgroup_enable_task_cg_lists() from missing set PF_EXITING and race against cgroup_exit(). Depending on the timing, cgroup_exit() may finish with the task still linked on css_set leading to list corruption. Fix it by grabbing siglock in cgroup_enable_task_cg_lists() so that PF_EXITING is guaranteed to be visible. This whole on-demand cg_list optimization is extremely fragile and has ample possibility to lead to bugs which can cause things like once-a-year oops during boot. I'm wondering whether the better approach would be just adding "cgroup_disable=all" handling which disables the whole cgroup rather than tempting fate with this on-demand craziness. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: stable@vger.kernel.org
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@ -2905,9 +2905,14 @@ static void cgroup_enable_task_cg_lists(void)
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* We should check if the process is exiting, otherwise
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* it will race with cgroup_exit() in that the list
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* entry won't be deleted though the process has exited.
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* Do it while holding siglock so that we don't end up
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* racing against cgroup_exit().
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*/
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spin_lock_irq(&p->sighand->siglock);
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if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
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list_add(&p->cg_list, &task_css_set(p)->tasks);
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spin_unlock_irq(&p->sighand->siglock);
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task_unlock(p);
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} while_each_thread(g, p);
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read_unlock(&tasklist_lock);
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