From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751275Ab3GXCVe (ORCPT ); Tue, 23 Jul 2013 22:21:34 -0400 Received: from moutng.kundenserver.de ([212.227.17.8]:60569 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750731Ab3GXCVd (ORCPT ); Tue, 23 Jul 2013 22:21:33 -0400 Message-ID: <1374632489.7333.18.camel@marge.simpson.net> Subject: Re: ptrace(PTRACE_ATTACH) [no intervering wait] ptrace(PTRACE_DETACH) may leave tracee stuck From: Mike Galbraith To: Oleg Nesterov Cc: LKML Date: Wed, 24 Jul 2013 04:21:29 +0200 In-Reply-To: <20130723155854.GA26211@redhat.com> References: <1374573914.30532.68.camel@marge.simpson.net> <20130723155854.GA26211@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-Provags-ID: V02:K0:AgRqZmkp3zmRIFsBxCwCfNkHQY7iIwmSGyiSqGwF4Nq sNdujq6EjDysqvirwqmgauZu13q8ftkBxFngPPrPeAvN+UmCuW cBG27ILR5Q4Q6hHTIMh5RS6GM79PKuTTvfgwyzIwu4Uigptfz5 z8cG2UKNprf8z+5o8RpaMBIFYC4G0tLhIOLRZxZf6/rsQ+gJxw d3THs4Dk34B3D+wYaVSzS3exNRkQFbmAZTCS4NTzLMWgwybzU6 sXcpwxjrnopLIkZdhS29hrF7kdG1W7pYX04FnbBNQLuPgsRF0m NZY+7NyGrQ9KBk+bdJbTrxexe36OyiljEQ1iYMyobuI30l/Al8 cJh6BSbYpd2QbA+kEMdZ0a0d/FN9s7/19aNMuK/sNibzZzraIW rlmFX+ki+NLTQ== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2013-07-23 at 17:58 +0200, Oleg Nesterov wrote: > On 07/23, Mike Galbraith wrote: > > > > I received a report that glibc:elf/pldd hangs occasionally, and indeed.. > > > > for i in `seq 1 1000`; do taskset -c 3 pldd $$ > /dev/null 2>&1; done > > > > ..will do so. Rummage..... > > > > ptrace(PTRACE_DETACH) returns -ESRCH when the trap hasn't happened yet, > > which happens because pldd doesn't wait() before ptrace(PTRACE_DETACH). > > > > pldd source: > > > [...snip...] > > > > Seems this usually works only because cycles expended between attach and > > detach is usually enough to let trap happen so tracee can set its state > > to TASK_TRACED as PTRACE_DETACH expects it to be. > > > > Is this expected behavior? > > Yes. PTRACE_ATTACH + PTRACE_DETACH is not correct without wait() in > between, this is expected. Thanks for confirmation. The man page was pretty clear (read it after slogging through source/traces, oh well, educational;) that -ESRCH was expected, but I wanted to be sure about tracee state thereafter. -Mike