On 2014/2/15 4:47, Tejun Heo wrote: > Currently, there's nothing explicitly preventing > cgroup_enable_task_cg_lists() from missing set PF_EXITING and race > against cgroup_exit(), and, depending on the timing, cgroup_exit() > seemingly may finish with the task still linked on css_set leading to > list corruption because cgroup_enable_task_cg_lists() can end up > linking it after list_empty(&tsk->cg_list) test in cgroup_exit(). > > This can't really happen because exit_mm() grabs and release > task_lock() between setting of PF_EXITING and cgroup_exit(), and > cgroup_enable_task_cg_lists() synchronizes against task_lock too; > however, this is fragile and more of a happy accident. Let's make the > synchronization explicit by making cgroup_enable_task_cg_lists() grab > siglock around PF_EXITING testing. > > 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 dynamic > optimization craziness. > > v2: Li pointed out that the race condition can't actually happen due > to task_lock locking in exit_mm(). Updated the patch description > accordingly and dropped -stable cc. >
I realise exit_mm() is a no-op for threads... There're quite a few places task_lock is used between exit_signal() and cgroup_exit(), but they're all conditional, so I think your original changelog stands! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
