netdev - Re: 2.6.30-rc6: Reported regressions from 2.6.29

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Message-ID: <20090518153115.GA22133@redhat.com>
Date:	Mon, 18 May 2009 17:31:15 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Jonathan Corbet <corbet@....net>, Martin Bammer <mrb74@....at>,
	Jeff Garzik <jgarzik@...ox.com>,
	Kumar Gala <galak@...nel.crashing.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Adrian Bunk <bunk@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Natalie Protasevich <protasnb@...il.com>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	Linux PM List <linux-pm@...ts.linux-foundation.org>,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	Linux Wireless List <linux-wireless@...r.kernel.org>,
	DRI <dri-devel@...ts.sourceforge.net>
Subject: Re: 2.6.30-rc6: Reported regressions from 2.6.29

On 05/18, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@...hat.com> wrote:
>
> > On 05/17, Ingo Molnar wrote:
> > >
> > > > 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>
> > >
> > > Oleg says in that thread that it's as-designed, and followup
> > > questions were not replied to (yet).
> >
> > Yes, I think this is false alarm. Perhaps I missed something, and
> > I am waiting for more info from Kumar, but it looks like ltp was
> > already changed to skip the "{ PTRACE_ATTACH, 1, EPERM }" test on
> > kernels after 2.6.25
>
> Btw., why did the patch (and the revert) make any difference to the
> test? Timing differences look improbable.

Because before this series /sbin/init always ignored SIGSTOP. Now,
ptracer does PTRACE_ATTACH and exits without clearing the pending
SIGSTOP. init dequeues this signal and becomes TASK_STOPPED.

Consider:

	$ sleep 1000 &
	[1] 875

	$ grep State: /proc/`pidof sleep`/status
	State:  S (sleeping)

	$ perl -e 'syscall 101, 16, 0+shift, 0,0' `pidof sleep`    # just PTRACE_ATTACH + exit

	[1]+  Stopped                 sleep 1000

	$ grep State: /proc/`pidof sleep`/status
	State:  T (stopped)

This is the "normal" behaviour, afaics the same happens with init now.

Oleg.

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