linux-kernel - Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE

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Message-ID: <20110214172358.GB14528@redhat.com>
Date:	Mon, 14 Feb 2011 18:23:58 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Roland McGrath <roland@...hat.com>, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after
	PTRACE_ATTACH

On 02/14, Tejun Heo wrote:
>
> On Mon, Feb 14, 2011 at 05:15:15PM +0100, Oleg Nesterov wrote:
> > > > PTRACE_CONT in this situation would do the same.
> > >
> > > This can be fixed by updating strace, right?  strace can look at the
> > > wait(2) exit code and if the tracee stopped for group stop, wait for
> > > the tracee to be continued instead of issuing PTRACE_SYSCALL.
> >
> > Yes, in this particular case strace could be more clever.
> >
> > But. The tracee should react to SIGCONT after that, this means we
> > shouldn't "delay" this stop or force the TASK_TRACED state.
>
> Yeap, which is achievable by treating group stop differently from
> ptrace traps and make it proceed to TASK_TRACED only if ptrace wants
> to issue commands.

Yes, agreed. And this is exactly what we currently do. Except, as you
pointed out, the simple s/STOPPED/TRACED/ change is buggy. But the fix
you suggested should be almost invisible to the userland.

> (reiterating just to make sure there's no
> misunderstanding)

The same from my side ;)

Oleg.

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