linux-kernel - Re: powerpc: fork && stepping (Was: [RFC,PATCH 0/14] utrace/ptrace)

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Message-ID: <20091127053925.GA8135@in.ibm.com>
Date:	Fri, 27 Nov 2009 11:09:25 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, utrace-devel@...hat.com,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: powerpc: fork && stepping (Was: [RFC,PATCH 0/14] utrace/ptrace)

On Thu, Nov 26, 2009 at 03:50:51PM +0100, Oleg Nesterov wrote:
> I changed the subject. This bug has nothing to do with utrace,
> the kernel fails with or without these changes.
> 
> On 11/26, Ananth N Mavinakayanahalli wrote:
> >
> > On Wed, Nov 25, 2009 at 04:40:52PM +0100, Oleg Nesterov wrote:
> > > On 11/25, Ananth N Mavinakayanahalli wrote:
> > > >
> > > > step-fork: step-fork.c:56: handler_fail: Assertion `0' failed.
> > > > /bin/sh: line 5: 24803 Aborted                 ${dir}$tst
> > > > FAIL: step-fork
> > >
> > > This is expected. Should be fixed by
> > >
> > > 	ptrace-copy_process-should-disable-stepping.patch
> > >
> > > in -mm tree. (I am attaching this patch below just in case)
> > > I din't mention this patch in this series because this bug
> > > is "ortogonal" to utrace/ptrace.
> >
> > The patch doesn't seem to fix the issue on powerpc:
> >
> > step-fork: step-fork.c:56: handler_fail: Assertion `0' failed.
> > /bin/sh: line 5: 17325 Aborted                 ${dir}$tst
> > FAIL: step-fork
> 
> Good to know, thanks again Ananth.
> 
> I'll take a look. Since I know nothing about powerpc, I can't
> promise the quick fix ;)
> 
> The bug was found by code inspection, but the fix is not trivial
> because it depends on arch/, and it turns out the arch-independent
> fix in
> 
> 	ptrace-copy_process-should-disable-stepping.patch
> 	http://marc.info/?l=linux-mm-commits&m=125789789322573
> 
> doesn't work.
> 
> Ananth, could you please run the test-case from the changelog
> below ? I do not really expect this can help, but just in case.

Right, it doesn't help :-(

GDB shows that the parent is forever struck at wait().

Ananth
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