Re: [PATCH] pids: make task_tgid_nr_ns() safe

[Peter Zijlstra]

On Mon, Aug 21, 2017 at 05:35:02PM +0200, 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.
> 
> We really need to change __unhash_process() to nullify group_leader,
> parent, and real_parent, but this needs some cleanups. Until then we
> can turn task_tgid_nr_ns() into another user of __task_pid_nr_ns() and
> fix the problem.
> 
> Reported-by: Troy Kensinger <tkensinger@xxxxxxxxxx>
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>