linux-kernel - Re: [PATCH] platform/x86/intel/vsec: Remove a useless mutex

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Message-ID: <b318af93-cbde-486d-854d-918b61795b1f@redhat.com>
Date: Sat, 2 Nov 2024 20:39:52 +0100
From: Hans de Goede <hdegoede@...hat.com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>,
 srinivas.pandruvada@...ux.intel.com,
 "David E. Box" <david.e.box@...ux.intel.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
 platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH] platform/x86/intel/vsec: Remove a useless mutex

Hi,

On 2-Nov-24 4:59 PM, Christophe JAILLET wrote:
> ida_alloc()/ida_free() don't need any mutex, so remove this one.
> 
> It was introduced by commit 9a90ea7d3784 ("platform/x86/intel/vsec: Use
> mutex for ida_alloc() and ida_free()").
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> See:
> https://elixir.bootlin.com/linux/v6.11.2/source/lib/idr.c#L375
> https://elixir.bootlin.com/linux/v6.11.2/source/lib/idr.c#L484
> 
> Review with care. This patch is clearly the opposite of the one in Fixes
> which states that locking IS needed.
> IIUC, idr_ functions need locking, but not ida_.
> 
> If I'm wrong, could you elaborate why? (because many other places will
> need to be fixed and the doc certainly needs updating)

This is my bad, looking at the ida docs they clearly state
no locking is necessary.

Back then I was working on / reviewing some other stuff using
idr which does need locking and I likely simply confused the 2
and suggested for the locking to be added.

Anyways dropping the locking looks good to me:

Reviewed-by: Hans de Goede <hdegoede@...hat.com>

Regards,

Hans



> ---
>  drivers/platform/x86/intel/vsec.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/drivers/platform/x86/intel/vsec.c b/drivers/platform/x86/intel/vsec.c
> index 7b5cc9993974..9e0f8e38178c 100644
> --- a/drivers/platform/x86/intel/vsec.c
> +++ b/drivers/platform/x86/intel/vsec.c
> @@ -79,17 +79,13 @@ static void intel_vsec_remove_aux(void *data)
>  	auxiliary_device_uninit(data);
>  }
>  
> -static DEFINE_MUTEX(vsec_ida_lock);
> -
>  static void intel_vsec_dev_release(struct device *dev)
>  {
>  	struct intel_vsec_device *intel_vsec_dev = dev_to_ivdev(dev);
>  
>  	xa_erase(&auxdev_array, intel_vsec_dev->id);
>  
> -	mutex_lock(&vsec_ida_lock);
>  	ida_free(intel_vsec_dev->ida, intel_vsec_dev->auxdev.id);
> -	mutex_unlock(&vsec_ida_lock);
>  
>  	kfree(intel_vsec_dev->resource);
>  	kfree(intel_vsec_dev);
> @@ -113,9 +109,7 @@ int intel_vsec_add_aux(struct pci_dev *pdev, struct device *parent,
>  		return ret;
>  	}
>  
> -	mutex_lock(&vsec_ida_lock);
>  	id = ida_alloc(intel_vsec_dev->ida, GFP_KERNEL);
> -	mutex_unlock(&vsec_ida_lock);
>  	if (id < 0) {
>  		xa_erase(&auxdev_array, intel_vsec_dev->id);
>  		kfree(intel_vsec_dev->resource);