From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:43768 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754268AbeDTIMd (ORCPT ); Fri, 20 Apr 2018 04:12:33 -0400 Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w3K89Nt1116520 for ; Fri, 20 Apr 2018 04:12:32 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0b-001b2d01.pphosted.com with ESMTP id 2hfb98beby-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Fri, 20 Apr 2018 04:12:32 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 20 Apr 2018 09:12:30 +0100 Date: Fri, 20 Apr 2018 10:12:26 +0200 From: Martin Schwidefsky Subject: Re: [RFC][PATCH] s390: add arch_change_pid for arch updates after task pid change In-Reply-To: <20180419160827.GB19917@redhat.com> References: <1524120286-19066-1-git-send-email-schwidefsky@de.ibm.com> <20180419140729.GA19917@redhat.com> <20180419162056.6b657d71@mschwideX1> <20180419160827.GB19917@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-Id: <20180420101226.377a281e@mschwideX1> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Oleg Nesterov Cc: linux-arch@vger.kernel.org, Andrew Morton On Thu, 19 Apr 2018 18:08:28 +0200 Oleg Nesterov wrote: > On 04/19, Martin Schwidefsky wrote: > > > > On Thu, 19 Apr 2018 16:07:29 +0200 > > Oleg Nesterov wrote: > > > > > On 04/19, Martin Schwidefsky wrote: > > > > > > > > In a multi-threaded program any thread can call execve(). If this > > > > is not done by the thread group leader, the de_thread() function > > > > replaces the pid of the task that calls execve() with the pid of > > > > thread group leader. If the task reaches user space again without > > > > going over __switch_to() the sampling tag is still set to the old > > > > pid. > > > > > > If this is the only reason for arch_change_pid() hook, then perhaps > > > it would be better/simpler to add it into de_thread() right after > > > change_pid(tsk, PIDTYPE_PID, task_pid(leader)) ? > > > > > > note also that this way arch_change_pid() doesn't need any checks and > > > any arguments, you can simply do > > > > > > void arch_change_pid(void) > > > { > > > S390_lowcore.current_pid = current->pid; > > > if (test_facility(40)) > > > lpp(&S390_lowcore.lpp); > > > } > > > > Yeah, the first patch I created to verify that this indeed the problem > > basically looked like your proposal. But then why not make it a more > > general hook for any kind of PID change? > > Well, I doubt very much we will ever need an arch-specific hook for > sys_setsid() or setpgid()... plus > > > Dunno if this is a worthwhile > > approach, the simpler version for sure works as well. > > and perhaps you can make another, even more simple change? can't you just > introduce the s390 version of arch_setup_new_exec, something like > > void arch_setup_new_exec(void) > { > if (S390_lowcore.current_pid != current->pid) { > S390_lowcore.current_pid = current->pid; > ... > } > } > > ? Nice, set_new_exec is called after flush_old_exec/de_thread. Yes, that should work as well and does not require a new arch hook. Thanks Oleg! -- blue skies, Martin. "Reality continues to ruin my life." - Calvin.