Re: [RFC PATCH] ARM: smp: Fix the CPU hotplug race with scheduler.

[Santosh Shilimkar]

On 6/21/2011 3:30 PM, Russell King - ARM Linux wrote:
> On Tue, Jun 21, 2011 at 02:38:34PM +0530, Santosh Shilimkar wrote:
> > Russell,
> >
> > On 6/20/2011 8:24 PM, Santosh Shilimkar wrote:
> > > On 6/20/2011 7:53 PM, Russell King - ARM Linux wrote:
> > > > So, as loops_per_jiffy is not local to this function, the compiler has
> > > > to write out that zero value, before calling calibrate_delay_converge(),
> > > > and loops_per_jiffy only becomes non-zero _after_
> > > > calibrate_delay_converge()
> > > > has returned. This opens the window and allows the spinlock debugging
> > > > code to explode.
> > > >
> > > > This patch closes the window completely, by only writing to
> > > > loops_per_jiffy
> > > > only when we have a real value for it.
> > > >
> > > > This allows me to boot 3.0.0-rc3 on Versatile Express (4 CPU) whereas
> > > > without this it fails with spinlock lockup and rcu problems.
> > > >
> > > > init/calibrate.c | 14 ++++++++------
> > > > 1 files changed, 8 insertions(+), 6 deletions(-)
> > > I am away from my board now. Will test this change.
> > Have tested your change and it seems to fix the crash I
> > was observing. Are you planning to send this fix for rc5?
>
> Yes.  I think sending CPUs into infinite loops in the spinlock code is
> definitely sufficiently serious that it needs to go to Linus ASAP.
> It'd be nice to have a tested-by line though.
Sure.

> > > btw, the online-active race is still open even with this patch close
> > > and should be fixed.
> > The only problem remains is waiting for active mask before
> > marking CPU online. Shall I refresh my patch with only
> > this change then ?
>
> I already have that as a separate change.
Can you point me to both of these commits so that I have
them in my tree for testing.

Thanks for help.

Regards
Santosh
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