Re: ptrace() hangs on attempt to seize/attach stopped & frozen task

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: ptrace() hangs on attempt to seize/attach stopped & frozen task
Date	2015-11-10 20:30 +0100
Message-ID	<qtmM9-MK-3@gated-at.bofh.it> (permalink)
References	<qsWoF-89v-3@gated-at.bofh.it> <qsYTw-18Q-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 11/09, Oleg Nesterov wrote:
>
> Hi,
>
> On 11/09, Andrey Ryabinin wrote:
> >
> > Hi,
> >
> > So, the ptrace() hangs if we try to attach to stopped task from freezing cgroup.
> > It seems this was introduced by 5d8f72b55c2756("freezer: change ptrace_stop/do_signal_stop to use freezable_schedule()").
>
> quite possible...

Not really, this was broken before that commit. Note that try_to_freeze()
was called under "relock:" label, so we had the same problem: the tracee
doesn't do do_jobctl_trap() after do_signal_stop() without try_to_freeze()
in between. Not that it matters, but still.

Oleg.

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Thread

ptrace() hangs on attempt to seize/attach stopped & frozen task Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-11-09 16:20 +0100
  Re: ptrace() hangs on attempt to seize/attach stopped & frozen task Oleg Nesterov <oleg@redhat.com> - 2015-11-09 19:00 +0100
    Re: ptrace() hangs on attempt to seize/attach stopped & frozen task Tejun Heo <tj@kernel.org> - 2015-11-09 19:10 +0100
      Re: ptrace() hangs on attempt to seize/attach stopped & frozen task Oleg Nesterov <oleg@redhat.com> - 2015-11-10 20:30 +0100
    Re: ptrace() hangs on attempt to seize/attach stopped & frozen task Oleg Nesterov <oleg@redhat.com> - 2015-11-10 20:30 +0100

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