Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757665AbZC0Pge (ORCPT ); Fri, 27 Mar 2009 11:36:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753045AbZC0PgY (ORCPT ); Fri, 27 Mar 2009 11:36:24 -0400 Received: from mga11.intel.com ([192.55.52.93]:17781 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750862AbZC0PgX convert rfc822-to-8bit (ORCPT ); Fri, 27 Mar 2009 11:36:23 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.38,432,1233561600"; d="scan'208";a="676539890" From: "Metzger, Markus T" To: Oleg Nesterov CC: "linux-kernel@vger.kernel.org" , "mingo@elte.hu" , "tglx@linutronix.de" , "hpa@zytor.com" , "markus.t.metzger@gmail.com" , "roland@redhat.com" , "eranian@googlemail.com" , "Villacis, Juan" , "ak@linux.jf.intel.com" Date: Fri, 27 Mar 2009 15:34:19 +0000 Subject: RE: [patch 3/14] x86, ptrace, bts: stop bts tracing early in do_exit Thread-Topic: [patch 3/14] x86, ptrace, bts: stop bts tracing early in do_exit Thread-Index: Acmu6Z6oWgYbhpJ7SvKPuhzGVRVnQwABedNQ Message-ID: <928CFBE8E7CB0040959E56B4EA41A77E9266B6D4@irsmsx504.ger.corp.intel.com> References: <20090327095525.A11052@sedona.ch.intel.com> <20090327143435.GD14504@redhat.com> In-Reply-To: <20090327143435.GD14504@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2065 Lines: 59 >-----Original Message----- >From: Oleg Nesterov [mailto:oleg@redhat.com] >Sent: Friday, March 27, 2009 3:35 PM >> +static void ptrace_bts_exit(void) >> +{ >> + if (unlikely(!list_empty(¤t->ptraced))) >> + ptrace_bts_exit_tracer(); >> + >> + if (unlikely(current->bts)) >> + ptrace_bts_exit_tracee(); >> +} > >Could you explain why do we need ptrace_bts_exit_tracee() ? > >If current is traced, the tracer should do ptrace_bts_release() >eventually, no? If current is traced and exits, it may be reaped by another thread that is not the tracer (that's actually your example you made in an earlier thread to describe the race between a normal detach and an exiting tracee). The ptrace_unlink() call to detach the tracer is executed with irq's disabled. I need irq's enabled (see the other discussion, to wait for the traced task). Therefore, I have the tracee disable bts tracing itself when it exits. >And if we really need to do ptrace_bts_exit_tracee(), then >"if (unlikely(current->bts))" check is racy. The tracer >can do PTRACE_BTS_CONFIG right after the check. The ptrace system call to do this would require the tracee to be stopped. regards, markus. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. -- 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/