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

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Date:	Thu, 12 Sep 2013 22:47:19 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	hpa@...ux.intel.com, david.vrabel@...rix.com,
	linux-kernel@...r.kernel.org, Stefano.Stabellini@...citrix.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH] xen: Do not enable spinlocks before jump_label_init()
 has executed

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.

Thanks,

-- Steve

> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> ---
>  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)
>  {

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