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

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Message-ID: <20151110201950.GA4925@redhat.com>
Date:	Tue, 10 Nov 2015 21:20:07 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:	Roland McGrath <roland@...k.frob.com>, Tejun Heo <tj@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: ptrace() hangs on attempt to seize/attach stopped & frozen task

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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