Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756800Ab0BKS5c (ORCPT ); Thu, 11 Feb 2010 13:57:32 -0500 Received: from mx1.redhat.com ([209.132.183.28]:6697 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756463Ab0BKS53 (ORCPT ); Thu, 11 Feb 2010 13:57:29 -0500 Date: Thu, 11 Feb 2010 19:55:30 +0100 From: Oleg Nesterov To: Salman Qazi Cc: taviso@google.com, Roland Dreier , Andrew Morton , Roland McGrath , linux-kernel@vger.kernel.org Subject: Re: Race in ptrace. Message-ID: <20100211185530.GA22055@redhat.com> References: <20100208221632.A7D6F9B33B@bumblebee1.mtv.corp.google.com> <20100208143231.6d804590.akpm@linux-foundation.org> <20100209112700.GA4258@redhat.com> <20100210133556.GA21925@redhat.com> <4352991a1002101038s6a2e67d9mc373416c17de9e6a@mail.gmail.com> <20100211125607.GA5086@redhat.com> <4352991a1002110832j1a4e6680scf4aa7effeb83a75@mail.gmail.com> <20100211165059.GA16053@redhat.com> <4352991a1002111043l35f1c1b5mcd9ad4c76f6351a7@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4352991a1002111043l35f1c1b5mcd9ad4c76f6351a7@mail.gmail.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: 915 Lines: 23 On 02/11, Salman Qazi wrote: > > >> > ? ? ? ? ? ? ? ?// the tracee is STOPPED as requested, not TRACED, > >> > ? ? ? ? ? ? ? ?// SIGCONT wakes it up > >> > ? ? ? ? ? ? ? ?kill(pid, SIGCONT); > > I am still missing something. There's probably a gap in my > understanding, so let's try to clarify it. The last "kill" call, > sends a SIGCONT. But, shouldn't this SIGCONT be intercepted by the > tracer before the tracee sees it? No. The tracee resumes (again: because it was STOPPED, not TRACED), dequeues SIGCONT, reports the signal and stops in TASK_TRACED, see ptrace_signal(). Meanwhile, until it calls ptrace_stop(), it is TASK_RUNNING and ptrace() fails. 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/