Re: Threads stuck in zap_pid_ns_processes()

From	ebiederm@xmission.com (Eric W. Biederman)
Newsgroups	linux.kernel
Subject	Re: Threads stuck in zap_pid_ns_processes()
Date	2017-05-12 15:40 +0200
Message-ID	<tGiXv-5aV-13@gated-at.bofh.it> (permalink)
References	(2 earlier) <tG2SJ-2Ew-1@gated-at.bofh.it> <tG3Yt-3hN-9@gated-at.bofh.it> <tG54d-3Ug-5@gated-at.bofh.it> <tG5GV-4qK-1@gated-at.bofh.it> <tGfdg-2rg-11@gated-at.bofh.it>
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Vovo Yang <vovoy@google.com> writes:

> On Fri, May 12, 2017 at 7:19 AM, Eric W. Biederman
> <ebiederm@xmission.com> wrote:
>> Guenter Roeck <linux@roeck-us.net> writes:
>>
>>> What I know so far is
>>> - We see this condition on a regular basis in the field. Regular is
>>>   relative, of course - let's say maybe 1 in a Milion Chromebooks
>>>   per day reports a crash because of it. That is not that many,
>>>   but it adds up.
>>> - We are able to reproduce the problem with a performance benchmark
>>>   which opens 100 chrome tabs. While that is a lot, it should not
>>>   result in a kernel hang/crash.
>>> - Vovo proviced the test code last night. I don't know if this is
>>>   exactly what is observed in the benchmark, or how it relates to the
>>>   benchmark in the first place, but it is the first time we are actually
>>>   able to reliably create a condition where the problem is seen.
>>
>> Thank you.  I will be interesting to hear what is happening in the
>> chrome perfomance benchmark that triggers this.
>>
> What's happening in the benchmark:
> 1. A chrome renderer process was created with CLONE_NEWPID
> 2. The process crashed
> 3. Chrome breakpad service calls ptrace(PTRACE_ATTACH, ..) to attach to every
>   threads of the crashed process to dump info
> 4. When breakpad detach the crashed process, the crashed process stuck in
>   zap_pid_ns_processes()

Very interesting thank you.

So the question is specifically which interaction is causing this.

In the test case provided it was a sibling task in the pid namespace
dying and not being reaped.  Which may be what is happening with
breakpad.  So far I have yet to see kernel bug but I won't rule one out.

Eric

Thread

Threads stuck in zap_pid_ns_processes() Guenter Roeck <linux@roeck-us.net> - 2017-05-11 19:20 +0200
  Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-11 19:40 +0200
    Re: Threads stuck in zap_pid_ns_processes() Guenter Roeck <linux@roeck-us.net> - 2017-05-11 20:40 +0200
      Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-11 22:30 +0200
        Re: Threads stuck in zap_pid_ns_processes() Guenter Roeck <linux@roeck-us.net> - 2017-05-11 22:50 +0200
          Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-11 23:50 +0200
    Re: Threads stuck in zap_pid_ns_processes() Guenter Roeck <linux@roeck-us.net> - 2017-05-11 22:30 +0200
      Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-11 23:40 +0200
        Re: Threads stuck in zap_pid_ns_processes() Guenter Roeck <linux@roeck-us.net> - 2017-05-12 00:50 +0200
          Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-12 01:30 +0200
            Re: Threads stuck in zap_pid_ns_processes() Vovo Yang <vovoy@google.com> - 2017-05-12 11:40 +0200
              Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-12 15:40 +0200
                Re: Threads stuck in zap_pid_ns_processes() Guenter Roeck <linux@roeck-us.net> - 2017-05-12 19:00 +0200
                Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-12 19:40 +0200
                [REVIEW][PATCH] pid_ns: Sleep in TASK_INTERRUPTIBLE in zap_pid_ns_processes ebiederm@xmission.com (Eric W. Biederman) - 2017-05-12 20:10 +0200
                Re: [REVIEW][PATCH] pid_ns: Sleep in TASK_INTERRUPTIBLE in  zap_pid_ns_processes Guenter Roeck <linux@roeck-us.net> - 2017-05-12 21:40 +0200
                Re: Threads stuck in zap_pid_ns_processes() Guenter Roeck <linux@roeck-us.net> - 2017-05-12 21:50 +0200
                Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-12 22:20 +0200
                Re: Threads stuck in zap_pid_ns_processes() Guenter Roeck <linux@roeck-us.net> - 2017-05-13 16:40 +0200
                Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-13 20:30 +0200
          Re: Threads stuck in zap_pid_ns_processes() ebiederm@xmission.com (Eric W. Biederman) - 2017-05-12 05:50 +0200

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