On 11/04, Andrew Morton wrote:
>
> On Wed, 4 Nov 2015 20:19:12 +0100 Oleg Nesterov <o...@redhat.com> wrote:
>
> > This explains WARN_ON(!JOBCTL_STOP_PENDING) in task_participate_group_stop()
> > triggered by the test-case from Dmitry:
> >
> > int main()
> > {
> > int pid = 1;
> > ptrace(PTRACE_ATTACH, pid, 0, 0);
> > ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_EXITKILL);
> > sleep(1);
> > return 0;
> > }
...
> > The test-case above needs root and (correctly) crashes the kernel,
> I'm thinking this should be backported into -stable due to WARN_ONs and
> kernel crashes.
Ah, sorry for confusion. The kernel crash is fine/correct. Debugger kills
init process, the exiting init calls panic(). With or without this patch.
BTW, I always thought we should remove this panic(), but this is off-topic.
After this patch the test-case above still crashes the kernel, but without
warning ;)
> And as f008faff0e27 is from 2009, that means all
> kernels.
Yes, I think this change is safe for -stable. But the only visible problem
is WARN_ON_ONCE() in task_participate_group_stop(), so I am not sure...
Well. Actually there are more problems. zap_threads(), de_thread() can be
fooled by signal_group_exit() == F too. So a multi-threaded /sbin/init can
miss SIGKILL if it does execve(), or if it starts the coredump. But only if
SIGKILL was private (sent by tkill).
I do not see any serious problem this patch could fix.
Oleg.
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