Re: [PATCH] xen/spinlock: Don't enable them unconditionally.

[Steven Rostedt]

On Fri,  4 Apr 2014 14:48:04 -0400
konrad@xxxxxxxxxx wrote:

> From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 
> The git commit a945928ea2709bc0e8e8165d33aed855a0110279
> ('xen: Do not enable spinlocks before jump_label_init() has executed')
> was added to deal with the jump machinery. Earlier the code
> that turned on the jump label was only called by Xen specific
> functions. But now that it had been moved to the initcall machinery
> it gets called on Xen, KVM, and baremetal - ouch!. And the detection
> machinery to only call it on Xen wasn't remembered in the heat
> of merge window excitement.
> 
> This means that the slowpath is enabled on baremetal while it should
> not be.
> 
> Reported-by: Waiman Long <waiman.long@xxxxxx>

Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

-- Steve

> CC: stable@xxxxxxxxxxxxxxx
> CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> CC: David Vrabel <david.vrabel@xxxxxxxxxx>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
>  arch/x86/xen/spinlock.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
> index 581521c..c570fea 100644
> --- a/arch/x86/xen/spinlock.c
> +++ b/arch/x86/xen/spinlock.c
> @@ -274,7 +274,7 @@ void __init xen_init_spinlocks(void)
>  		printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
>  		return;
>  	}
> -
> +	printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
>  	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
>  	pv_lock_ops.unlock_kick = xen_unlock_kick;
>  }
> @@ -290,6 +290,9 @@ static __init int xen_init_spinlocks_jump(void)
>  	if (!xen_pvspin)
>  		return 0;
>  
> +	if (!xen_domain())
> +		return 0;
> +
>  	static_key_slow_inc(&paravirt_ticketlocks_enabled);
>  	return 0;
>  }

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