linux-kernel - Re: [Bug #13107] LTP 20080131 causes defunct processes w/2.6.30-rc1

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Message-ID: <20090518175410.GA2713@us.ibm.com>
Date:	Mon, 18 May 2009 10:54:10 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kumar Gala <galak@...nel.crashing.org>,
	Roland McGrath <roland@...hat.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [Bug #13107] LTP 20080131 causes defunct processes w/2.6.30-rc1

Oleg Nesterov [oleg@...hat.com] wrote:
| Sorry for delay, I had a vacation.
| 
| On 05/17, Linus Torvalds wrote:
| >
| > On Sat, 16 May 2009, Rafael J. Wysocki wrote:
| > >
| > > This message has been generated automatically as a part of a report
| > > of recent regressions.
| > >
| > > The following bug entry is on the current list of known regressions
| > > from 2.6.29.  Please verify if it still should be listed and let me know
| > > (either way).
| > >
| > >
| > > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=13107
| > > Subject		: LTP 20080131 causes defunct processes w/2.6.30-rc1
| > > Submitter	: Kumar Gala <galak@...nel.crashing.org>
| > > Date		: 2009-04-09 15:43 (38 days old)
| > > First-Bad-Commit: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b3bfa0cba867f23365b81658b47efd906830879b
| > > References	: http://marc.info/?l=linux-kernel&m=123929187208953&w=4
| > > 		  http://lkml.org/lkml/2009/4/10/193
| > > Handled-By	: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
| >
| > I think we have to revert that thing. I haven't heard of any fixes to that
| > commit.
| 
| I thought this was already resolved.

Yes, so did I. We had asked for more info/confirmation before, most recently
on Apr 25 http://lkml.org/lkml/2009/4/25/132, although finding the LTP
test like below would have helped :-)

| 
| And I don't think the kernel is buggy, this is expected behaviour. With
| this commit (actually, there were several patches) /sbin/init respects
| SIGSTOP if the caller has rights to send it, this change is intentional.
| I'd even say this is fix.
| 
| Note that even root can't stop init, SIGSTOP should be sent from the
| parent namespace, or from ptracer. And ptracer could obviously ptrace_stop()
| init even before this patch.
| 
| 
| But, Kumar, could you please provide more info? I downloaded
| ltp-full-20081130.tgz, and I see that ptrace03.c does:

I beleive Kumar was running an older version of LTP (20080131)

| 
|                         /* since Linux 2.6.26, it's allowed to trace init,
|                            so just skip this test case */
|                         if (i == 0 && tst_kvercmp(2,6,25) > 0) {
|                                 tst_resm(TCONF,
|                                          "this kernel allows to trace init");
|                                 continue;
|                         }
| 
| So, could you explain which test traces init?
| 
| Oleg.
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