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

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Message-ID: <20091128070602.GA23108@in.ibm.com>
Date:	Sat, 28 Nov 2009 12:36:02 +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>,
	Veaceslav Falico <vfalico@...hat.com>
Subject: Re: powerpc: fork && stepping (Was: [RFC,PATCH 0/14] utrace/ptrace)

On Fri, Nov 27, 2009 at 04:05:31PM +0100, Oleg Nesterov wrote:
> On 11/27, Ananth N Mavinakayanahalli wrote:
> >
> > On Thu, Nov 26, 2009 at 03:50:51PM +0100, Oleg Nesterov wrote:
> >
> > > 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().
> 
> Now this is interesting. Could you please double check the parent hangs
> in wait() ?
> 
> This doesn't match the testing we did on powerpc machine with Veaceslav,
> and I hoped the problem was already resolved?
> 
> Please see other emails in this thread.
> 
> 
> Hmm. Fortunately I still have the access to the testing machine.
> Yes, according to gdb it looks as if it "hangs" in wait(). This
> is not true. You can strace gdb itself, or look at xxx_ctxt_switches
> in /proc/pid_of_parent/status.
> 
> Better yet, do not use gdb at all. Just strace (without -f) the parent,
> you should see it continues to trace the child and loops forever.

Yes, I can see it looping.

However, Veaceslav's modified testcase in
http://lkml.org/lkml/2009/11/27/215 passes on the machine with
ptrace-copy_process-should-disable-stepping.patch.

Ananth
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