Date: Wed, 23 Feb 2011 17:44:27 +0100
From: Jan Kratochvil <jan.kratochvil@redhat.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>, Tejun Heo <tj@kernel.org>,
        Roland McGrath <roland@redhat.com>, linux-kernel@vger.kernel.org,
        torvalds@linux-foundation.org, akpm@linux-foundation.org
Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after
 PTRACE_ATTACH
Message-ID: <20110223164427.GA22359@host1.dyn.jankratochvil.net>
References: <20110219201603.GB8662@redhat.com>
 <20110219200637.GA8662@redhat.com>
 <20110220094050.GA7714@host1.dyn.jankratochvil.net>
 <20110220171658.GA27355@redhat.com>
 <20110220185204.GA14737@host1.dyn.jankratochvil.net>
 <20110220203819.GB32682@redhat.com>
 <20110220212053.GA23412@host1.dyn.jankratochvil.net>
 <20110221142325.GA16664@redhat.com>
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On Mon, 21 Feb 2011 15:23:25 +0100, Oleg Nesterov wrote:
> On 02/20, Jan Kratochvil wrote:
> > Now if new GDB should allow inferior functions calls on previously
> > `(T) stopped' process doing PTRACE_CONT(SIGCONT)
> 
> No, no, this won't work. You need to send SIGCONT via kill/tkill. Once
> again, we can add the special case for PTRACE_CONT(SIGCONT), but please
> look at Roland's comment: http://marc.info/?l=linux-kernel&m=129796917823181
> 
> And given that currently gdb does PTRACE_CONT(0) this special case can't
> help anyway unless you change gdb.

I would better play with a patched kernel.


> > but how to make it `(T) stopped' afterwards?  PTRACE_CONT(SIGSTOP)
> > right after the inferior call will make the old kernels run the inferior - we
> > do not want that.
> 
> Hmm... probably I am totally confused... but PTRACE_CONT(SIGSTOP)
> should work in this case, the tracee reports SIGTRAP after the single-step
> (if I understand correctly how gdb implements this).

The inferior call returns to a breakpoint (0xcc), this is the reason of the
SIGTRAP at the end.  I expect PTRACE_CONT(SIGSTOP) could work even in such
case.


Thanks,
Jan
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