Re: [PATCH] xen: Do not enable spinlocks before jump_label_init() hasexecuted

[Boris Ostrovsky]

On 09/12/2013 10:47 PM, Steven Rostedt wrote:
> On Thu, 12 Sep 2013 22:29:44 -0400
> Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
>
> > From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> >
> > xen_init_spinlocks() currently calls static_key_slow_inc() before
> > jump_label_init() is invoked. When CONFIG_JUMP_LABEL is set (which usually is
> > the case) the effect of this static_key_slow_inc() is deferred until after
> > jump_label_init(). This is different from when CONFIG_JUMP_LABEL is not set, in
> > which case the key is set immediately. Thus, depending on the value of config
> > option, we may observe different behavior.
> >
> > In addition, when we come to __jump_label_transform() from jump_label_init(),
> > the key (paravirt_ticketlocks_enabled) is already enabled. On processors where
> > ideal_nop is not the same as default_nop this will cause a BUG() since it is
> > expected that before a key is enabled the latter is replaced by the former
> > during initialization.
> >
> > To address this problem we need to move
> > static_key_slow_inc(&paravirt_ticketlocks_enabled) so that it is called
> > after jump_label_init(). We also need to make sure that this is done before
> > other cpus start to boot. early_initcall appears to be  a good place to do so.
> > (Note that we cannot move whole xen_init_spinlocks() there since pv_lock_ops
> > need to be set before alternative_instructions() runs.)
> Reviewed-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
>
> Peter,
>
> This fixes a regression in 3.12 against xen. Please pull and push to
> Linus sometime soon.

Peter,

Are you planning on taking this patch?

Thanks.
-boris


> Thanks,
>
> -- Steve
>
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > ---
> >   arch/x86/xen/spinlock.c | 11 +++++++++--
> >   1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
> > index 253f63f..d90628d 100644
> > --- a/arch/x86/xen/spinlock.c
> > +++ b/arch/x86/xen/spinlock.c
> > @@ -267,11 +267,18 @@ void __init xen_init_spinlocks(void)
> >   		return;
> >   	}
> >   
> > -	static_key_slow_inc(&paravirt_ticketlocks_enabled);
> > -
> >   	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
> >   	pv_lock_ops.unlock_kick = xen_unlock_kick;
> >   }
> > +static __init int xen_init_spinlocks_jump(void)
> > +{
> > +	if (!xen_pvspin)
> > +		return 0;
> > +
> > +	static_key_slow_inc(&paravirt_ticketlocks_enabled);
> > +	return 0;
> > +}
> > +early_initcall(xen_init_spinlocks_jump);
> >   
> >   static __init int xen_parse_nopvspin(char *arg)
> >   {

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/