linux-kernel - Re: [PATCH 2/2] oom: kill the insufficient and no longer needed PT_TRACE

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Date:	Tue, 2 Dec 2014 19:05:29 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Cong Wang <xiyou.wangcong@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] oom: kill the insufficient and no longer needed
	PT_TRACE_EXIT check

On 12/02, Michal Hocko wrote:
>
> On Fri 28-11-14 00:04:08, Oleg Nesterov wrote:
> > After the previous patch we can remove the PT_TRACE_EXIT check in
> > oom_scan_process_thread(), it was added to handle the case when the
> > coredumping was "frozen" by ptrace, but it doesn't really work. If
> > nothing else, we would need to check all threads which could share
> > the same ->mm to make it more or less correct.
> >
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
>
> I still do not see why we do not need task->ptrace & PT_TRACE_EXIT check
> here. I do understand that the check on group_leader doesn't make much
> sense. ptrace_event would block until the tracer let the task run again
> which may be never AFAICS.

No, note that PT_TRACE_EXIT (the last ptrace event) is reported before
PF_EXITING is set.

(just in case... we do have some problems with SIGKILL && ptrace, but
 this is completely off-topic and has nothing to do with oom-kill.c)

Oleg.

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