exit: wait: don't use zombie->real_parent
1. wait_task_zombie() uses p->real_parent to get psig/siglock. This is correct but needs tasklist_lock, ->real_parent can exit. We can use "current" instead. This is our natural child, its parent must be our sub-thread. 2. Read psig/sig outside of ->siglock, ->signal is no longer protected by this lock. 3. Fix the outdated comments about tasklist_lock. We can not race with __exit_signal(), the whole thread group is dead, nobody but us can call it. Also clarify the usage of ->stats_lock and ->siglock. Note: thread_group_cputime_adjusted() is sub-optimal in this case, we probably want to export cputime_adjust() to avoid thread_group_cputime(). The comment says "all threads" but there are no other threads. Signed-off-by: NOleg Nesterov <oleg@redhat.com> Cc: Aaron Tomlin <atomlin@redhat.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Rik van Riel <riel@redhat.com> Cc: Sterling Alexander <stalexan@redhat.com> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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