linux-kernel - Re: Threads stuck in zap_pid_ns

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Message-ID: <87inkfab4l.fsf@xmission.com>
Date:   Thu, 01 Jun 2017 12:08:58 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Vovo Yang <vovoy@...gle.com>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: Threads stuck in zap_pid_ns_processes()

Guenter Roeck <linux@...ck-us.net> writes:
>
> I think you nailed it. If I drop CLONE_NEWPID from the reproducer I get
> a zombie process.
>
> I guess the only question left is if zap_pid_ns_processes() should (or could)
> somehow detect that situation and return instead of waiting forever.
> What do you think ?

Any chance you can point me at the chromium code that is performing the
ptrace?

I want to conduct a review of the kernel semantics to see if the current
semantics make it unnecessarily easy to get into hang situations.  If
the semantics make it really easy to get into a hang situation I want
to see if there is anything we can do to delicately change the semantics
to avoid the hangs without breaking existing userspace.

We have a real problem in exec which has similar semantics and as long
as I am looking at one I figure I should look at the other.

Eric