tree 96b5e5466504cc8c88b0f0435e80f70f0c627c58
parent 14ccee78fc82f5512908f4424f541549a5705b89
author Oleg Nesterov <oleg@redhat.com> 1503329702 +0200
committer Linus Torvalds <torvalds@linux-foundation.org> 1503344851 -0700

pids: make task_tgid_nr_ns() safe

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@google.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>