On Mon, Aug 21, 2017 at 05:36:27PM +0200, Oleg Nesterov wrote: > On 08/21, Oleg Nesterov wrote: > > > > This was reported many times, and this was even mentioned in commit > > 52ee2dfdd4f5 "pids: refactor vnr/nr_ns helpers to make them safe" but > > somehow nobody bothered to fix the obvious problem: task_tgid_nr_ns() > > is not safe because task->group_leader points to nowhere after the > > exiting task passes exit_notify(), rcu_read_lock() can not help. > > Peter, > > we already discussed this before, but I can't recall the result... > > perf_event_pid() can hit this problem too, with this patch the problem > goes away but (with or without this patch) we do not want to report zero > pids to avoid the confusion with idle threads, right? > > So do you think the patch below makes sense or we do not care?
Yeah, works for me. While rare I think it makes sense to distinguish between a recently dead and the idle tasks.
