This is the temporary simple fix for 3.2, we need more changes in this
area.
1. do_signal_stop() assumes that the running untraced thread in the
stopped thread group is not possible. This was our goal but it is
not yet achieved: a stopped-but-resumed tracee can clone the running
thread which can initiate another group-stop.
Remove WARN_ON_ONCE(!current->ptrace).
2. A new thread always starts with ->jobctl = 0. If it is auto-attached
and this group is stopped, __ptrace_unlink() sets JOBCTL_STOP_PENDING
but JOBCTL_STOP_SIGMASK part is zero, this triggers WANR_ON(!signr)
in do_jobctl_trap() if another debugger attaches.
Change __ptrace_unlink() to set the artificial SIGSTOP for report.
Alternatively we could change ptrace_init_task() to copy signr from
current, but this means we can copy it for no reason and hide the
possible similar problems.
Acked-by: Tejun Heo <tj@kernel.org>
Cc: <stable@kernel.org> [3.1]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
