linux-kernel - Re: [PATCH] xen: Do not enable spinlocks before jump_label

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Date:	Tue, 24 Sep 2013 16:11:33 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	hpa@...ux.intel.com, Steven Rostedt <rostedt@...dmis.org>,
	david.vrabel@...rix.com, linux-kernel@...r.kernel.org,
	Stefano.Stabellini@...citrix.com
Subject: Re: [PATCH] xen: Do not enable spinlocks before jump_label_init()
 has executed

On Tue, Sep 24, 2013 at 12:50:45PM -0700, Boris Ostrovsky wrote:
> On 09/12/2013 10:47 PM, Steven Rostedt wrote:
> >On Thu, 12 Sep 2013 22:29:44 -0400
> >Boris Ostrovsky <boris.ostrovsky@...cle.com> wrote:
> >
> >>From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> >>
> >>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@...dmis.org>
> >
> >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?

If he hasn't done yet (and I don't see a tip-bot email so I think the answer
is no) I can do it (as I am back from my mini vacation).

Thanks for the ping!
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