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

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] pids: make task_tgid_nr_ns() safe
Date	2017-08-21 22:10 +0200
Message-ID	<uh1bk-tH-17@gated-at.bofh.it> (permalink)
References	(2 earlier) <ugWY2-67r-13@gated-at.bofh.it> <ugWY2-67r-15@gated-at.bofh.it> <ugWY2-67r-17@gated-at.bofh.it> <ugWY2-67r-19@gated-at.bofh.it> <ugWY2-67r-7@gated-at.bofh.it>
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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@google.com>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

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[PATCH] pids: make task_tgid_nr_ns() safe Oleg Nesterov <oleg@redhat.com> - 2017-08-21 17:40 +0200
  perf_event_pid() (Was: [PATCH] pids: make task_tgid_nr_ns() safe) Oleg Nesterov <oleg@redhat.com> - 2017-08-21 17:40 +0200
    Re: perf_event_pid() (Was: [PATCH] pids: make task_tgid_nr_ns() safe) Peter Zijlstra <peterz@infradead.org> - 2017-08-21 21:20 +0200
  Re: [PATCH] pids: make task_tgid_nr_ns() safe Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-21 21:50 +0200
    Re: [PATCH] pids: make task_tgid_nr_ns() safe Oleg Nesterov <oleg@redhat.com> - 2017-08-22 14:30 +0200
  Re: [PATCH] pids: make task_tgid_nr_ns() safe Peter Zijlstra <peterz@infradead.org> - 2017-08-21 22:10 +0200

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