DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=googlemail.com; s=gamma;
        h=mime-version:in-reply-to:references:from:date:message-id:subject:to
         :cc:content-type:content-transfer-encoding;
        b=qADAJ6gWNTyrkndZO432aaQfX7Wtop30HDMwHBTiQXIC9OxOsHuPnMXLrQtB0B3pgj
         JTl6EFCp4NenwaJ7MeQ8EDq0zFenpHicY5djLBCsanpx2idN8tzqeLtxjtgBaglBJebE
         KZeqZgyoopHPaMxFAoWlRW3JHv1vGWkUGNrDk=
MIME-Version: 1.0
In-Reply-To: <6b211a19ed02fa7f001343fbd8e3d5a9.squirrel@webmail.greenhost.nl>
References: <20110301152457.GE26074@htj.dyndns.org> <201103011757.48593.vda.linux@googlemail.com>
 <20110301170953.GB17933@htj.dyndns.org> <AANLkTi=8=Tw2aYzvwM_s8dsMmw3W_tYjsYkqTHS9moUW@mail.gmail.com>
 <20110301183454.GC23527@mtj.dyndns.org> <830cc1666bd4a610d5e870218f06bd2d.squirrel@webmail.greenhost.nl>
 <20110302074447.GE19669@htj.dyndns.org> <6b211a19ed02fa7f001343fbd8e3d5a9.squirrel@webmail.greenhost.nl>
From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Wed, 2 Mar 2011 12:52:36 +0100
Message-ID: <AANLkTinTaSpDk=89VoNrZBhCixX6dGdT4R=R9d=FG1=3@mail.gmail.com>
Subject: Re: [RFC] Proposal for ptrace improvements
To: Indan Zupancic <indan@nul.nu>
Cc: Tejun Heo <tj@kernel.org>, Oleg Nesterov <oleg@redhat.com>,
        Roland McGrath <roland@redhat.com>, jan.kratochvil@redhat.com,
        linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
        akpm@linux-foundation.org
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1462
Lines: 32

On Wed, Mar 2, 2011 at 12:32 PM, Indan Zupancic <indan@nul.nu> wrote:
> On Wed, March 2, 2011 08:44, Tejun Heo wrote:
>> On Wed, Mar 02, 2011 at 06:07:35AM +0100, Indan Zupancic wrote:
>>> I'm not sure what Denys is talking about: Currently it's impossible to
>>> pass along SIGSTOP to traced processes. Quoting the ptrace manpage:
>>>
>>> ? ?PTRACE_CONT
>>> ? ? ? ? ? Restarts ?the stopped child process. ?If data is nonzero and not
>>> ? ? ? ? ? SIGSTOP, it is interpreted as a signal to be ?delivered ?to ?the
>>> ? ? ? ? ? child; ?otherwise, ?no ?signal is delivered.
>>
>> AFAICS, that's not true. ?SIGSTOP isn't treated differently from other
>> signals in the ptrace signal delivery path. ?Maybe it was true in the
>> past.
>
> Well, I can't find it in the code either, but it's probably a side-effect
> of how ptrace is currently implemented. Test program code below, see for
> yourself. I hope it's a program bug, but perhaps it's a kernel bug, as I
> seem to get two SIGSTOP events when I allow the SIGSTOP, but only one when
> denying it.

This was discussed recently (again). Second SIGSTOP you see
is a job control stop notification (as opposed to signal delivery notification).
It's not a bug.

-- 
vda
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/