Re: [PATCH -mm v2 1/3] mm/oom_kill: remove the wrong fatal_signal_pending() check in oom_kill_process()

[Oleg Nesterov]

On 10/01, Michal Hocko wrote:
>
> On Wed 30-09-15 20:24:05, Oleg Nesterov wrote:
> [...]
> > It is possible that the group leader
> > has the pending SIGKILL because its sub-thread originated the coredump,
> > in this case we must not skip this process.
>
> I do not understand this. If the group leader has SIGKILL pending it
> will die anyway regardless whether we send another sigkill or not, no?

Yes it will die, but only after the coredump is finished.

Suppose we have a thread group with the group leader P and another
thread T. If T starts the coredump, it sends SIGKILL to P and waits
until it parks in exit_mm(). Then T actually dumps the core which may
need more memory, a lot of time, etc.

We need to kill this process. Yes, P is already killed and it sleeps
in TASK_UNINTERRUPTIBLE so this thread does not need SIGKILL. But
do_send_sig_info(P) will also find T and kill it too to make
dump_interrupted() == T.

Oleg.

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