linux-kernel - Re: [PATCH 1/1] drm/amdkfd: Protect the Client whilst it is being operated on

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Message-ID: <YjNDdXXOMYNuHJcV@google.com>
Date:   Thu, 17 Mar 2022 14:19:33 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     linux-kernel@...r.kernel.org,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 1/1] drm/amdkfd: Protect the Client whilst it is being
 operated on

On Thu, 17 Mar 2022, Lee Jones wrote:

> Presently the Client can be freed whilst still in use.
> 
> Use the already provided lock to prevent this.
> 
> Cc: Felix Kuehling <Felix.Kuehling@....com>
> Cc: Alex Deucher <alexander.deucher@....com>
> Cc: "Christian König" <christian.koenig@....com>
> Cc: "Pan, Xinhui" <Xinhui.Pan@....com>
> Cc: David Airlie <airlied@...ux.ie>
> Cc: Daniel Vetter <daniel@...ll.ch>
> Cc: amd-gfx@...ts.freedesktop.org
> Cc: dri-devel@...ts.freedesktop.org
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---

I should have clarified here, that:

This patch has only been *build* tested.

Since I have no way to run this on real H/W.

Please ensure this is tested on real H/W before it gets applied, since
it *may* have some undesired side-effects.  For instance, I have no
idea if client->lock plays nicely with dev->smi_lock or whether this
may well end up in deadlock.

TIA.

>  drivers/gpu/drm/amd/amdkfd/kfd_smi_events.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_smi_events.c b/drivers/gpu/drm/amd/amdkfd/kfd_smi_events.c
> index e4beebb1c80a2..3b9ac1e87231f 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_smi_events.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_smi_events.c
> @@ -145,8 +145,11 @@ static int kfd_smi_ev_release(struct inode *inode, struct file *filep)
>  	spin_unlock(&dev->smi_lock);
>  
>  	synchronize_rcu();
> +
> +	spin_lock(&client->lock);
>  	kfifo_free(&client->fifo);
>  	kfree(client);
> +	spin_unlock(&client->lock);
>  
>  	return 0;
>  }
> @@ -247,11 +250,13 @@ int kfd_smi_event_open(struct kfd_dev *dev, uint32_t *fd)
>  		return ret;
>  	}
>  
> +	spin_lock(&client->lock);
>  	ret = anon_inode_getfd(kfd_smi_name, &kfd_smi_ev_fops, (void *)client,
>  			       O_RDWR);
>  	if (ret < 0) {
>  		kfifo_free(&client->fifo);
>  		kfree(client);
> +		spin_unlock(&client->lock);
>  		return ret;
>  	}
>  	*fd = ret;
> @@ -264,6 +269,7 @@ int kfd_smi_event_open(struct kfd_dev *dev, uint32_t *fd)
>  	spin_lock(&dev->smi_lock);
>  	list_add_rcu(&client->list, &dev->smi_clients);
>  	spin_unlock(&dev->smi_lock);
> +	spin_unlock(&client->lock);
>  
>  	return 0;
>  }

-- 
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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