Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932521AbZLNUav (ORCPT ); Mon, 14 Dec 2009 15:30:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932273AbZLNUar (ORCPT ); Mon, 14 Dec 2009 15:30:47 -0500 Received: from mx1.redhat.com ([209.132.183.28]:26709 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932502AbZLNUaq (ORCPT ); Mon, 14 Dec 2009 15:30:46 -0500 Date: Mon, 14 Dec 2009 21:24:54 +0100 From: Oleg Nesterov To: Roland McGrath Cc: Peter Zijlstra , Alexey Dobriyan , Ananth Mavinakayanahalli , Christoph Hellwig , "Frank Ch. Eigler" , Ingo Molnar , linux-kernel@vger.kernel.org, utrace-devel@redhat.com Subject: Re: [RFC,PATCH 14/14] utrace core Message-ID: <20091214202454.GA16124@redhat.com> References: <20091124200220.GA5828@redhat.com> <1259697242.1697.1075.camel@laptop> <20091214002533.3052519@magilla.sf.frob.com> <20091214170327.GA7666@redhat.com> <20091214194441.4D6BFE24E@magilla.sf.frob.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091214194441.4D6BFE24E@magilla.sf.frob.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1163 Lines: 29 On 12/14, Roland McGrath wrote: > > > > In the stopped cases, there are lots of locks and barriers and things > > > after resuming. (Oleg?) > > > > Every time the tracee resumes after TASK_TRACED it uses utrace->lock > > to synchronize with utrace_control/etc, it must see any changes. > > And TASK_STOPPED? SIGCONT can wake up the TASK_STOPPED tracee. I don't think the tracer should ever rely on TASK_STOPPED (utrace never does). If the tracer needs the "really stopped" tracee we have UTRACE_STOP, and this means TASK_TRACED. But I am not sure I understand this part of discussion... In any case the tracee should see any changes which were done before the wakeup. But TASK_STOPPED can't guarantee the tracee won't be resumed until the tracer wakes it up. Of course, TASK_TRACED can't prevent SIGKILL, but in this case we should only care about "the tracee can't resume until we drop utrace->lock" case. Oleg. -- 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/