From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754818Ab0BAOVL (ORCPT ); Mon, 1 Feb 2010 09:21:11 -0500 Received: from mx1.redhat.com ([209.132.183.28]:28574 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753531Ab0BAOVJ (ORCPT ); Mon, 1 Feb 2010 09:21:09 -0500 Date: Mon, 1 Feb 2010 15:18:56 +0100 From: Oleg Nesterov To: Neil Horman Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, jmoskovc@redhat.com, mingo@redhat.com, drbd-dev@lists.linbit.com, benh@kernel.crashing.org, t.sailer@alumni.ethz.ch, abelay@mit.edu, gregkh@suse.de, spock@gentoo.org, viro@zeniv.linux.org.uk, neilb@suse.de, mfasheh@suse.com, menage@google.com, shemminger@linux-foundation.org, takedakn@nttdata.co.jp Subject: Re: [PATCH 2/2] exec: allow core_pipe recursion check to look for a value of 1 rather than 0 (v2) Message-ID: <20100201141856.GA9453@redhat.com> References: <20100121200806.GA29801@shamino.rdu.redhat.com> <20100129151024.GA19249@hmsreliant.think-freely.org> <20100129151458.GC19249@hmsreliant.think-freely.org> <20100131155000.GB13402@redhat.com> <20100131160030.GB1950@localhost.localdomain> <20100201102936.GA31611@redhat.com> <20100201131627.GE25094@hmsreliant.think-freely.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100201131627.GE25094@hmsreliant.think-freely.org> 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 On 02/01, Neil Horman wrote: > > On Mon, Feb 01, 2010 at 11:29:36AM +0100, Oleg Nesterov wrote: > > > > > > Completely off-topic, but I think __call_usermodehelper(UMH_NO_WAIT) is > > > > buggy. if kernel_thread() failes it should do call_usermodehelper_freeinfo(). > > > > Also, UMH_WAIT_EXEC should set ->retval in this case. > > > > > > > I went down that path last time I changed this code, Andrew and I decided that > > > yes it was buggy, but someone (can't recall how) smacked me around a bit and > > > explained how it worked (some odd artifact behavior of the scheduler). Its in > > > the lkml archives if you want to get the whole story. > > > > Hmm. I strongly believe this is buggy, and the scheduler can't help in any > > way. Fortunately, kernel_thread() must "never" fail... > > Commit 95e0d86badc410d525ea7218fd32df7bfbf9c837 has the discussion from the > previous time that I messed with this code. Not sure how closely it relates, > but... The changelog correctly explains why it is OK to do complete() from __call_usermodehelper() in UMH_WAIT_EXEC case: CLONE_VFORK guarantees kernel_thread(CLONE_VFORK) won't return (see do_fork()) until ____call_usermodehelper() thread does exec or exits. I meant a much more simple problem, I think we need something like this patch: --- kernel/kmod.c +++ kernel/kmod.c @@ -266,15 +266,18 @@ static void __call_usermodehelper(struct switch (wait) { case UMH_NO_WAIT: + if (pid < 0) + call_usermodehelper_freeinfo(sub_info); break; case UMH_WAIT_PROC: if (pid > 0) break; - sub_info->retval = pid; /* FALLTHROUGH */ case UMH_WAIT_EXEC: + if (pid < 0) + sub_info->retval = pid; complete(sub_info->complete); } } to fix 2 problems if kernel_thread() fails in __call_usermodehelper() - UMH_NO_WAIT should do call_usermodehelper_freeinfo() - UMH_WAIT_EXEC should set sub_info->retval to indicate the error > > Oh. And in theory, it is better to change wait_for_helper(). It should > > do allow_signal(SIGCHLD) after kernel_thread(). I was wrong, of course we can't do this, the child can exit and reap itself before we do sys_wait4(). > Otherwise, kernel_thread() > > can fail if user-space sends SIGCHLD to the forking thread. but this is still true. Fortunately this is very minor problem. Oleg.