linux-kernel - Re: [PATCH v5 2/3] kernel/resource: Refactor __request

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Date:   Tue, 20 Apr 2021 16:43:35 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Alistair Popple <apopple@...dia.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        daniel.vetter@...ll.ch, dan.j.williams@...el.com,
        gregkh@...uxfoundation.org, jhubbard@...dia.com,
        jglisse@...hat.com, bsingharora@...il.com, smuchun@...il.com
Subject: Re: [PATCH v5 2/3] kernel/resource: Refactor __request_region to
 allow external locking

On 19.04.21 09:01, Alistair Popple wrote:
> Refactor the portion of __request_region() done whilst holding the
> resource_lock into a separate function to allow callers to hold the
> lock.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> ---
>   kernel/resource.c | 52 +++++++++++++++++++++++++++++------------------
>   1 file changed, 32 insertions(+), 20 deletions(-)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 736768587d2d..75f8da722497 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -1181,31 +1181,16 @@ struct address_space *iomem_get_mapping(void)
>   	return smp_load_acquire(&iomem_inode)->i_mapping;
>   }
>   
> -/**
> - * __request_region - create a new busy resource region
> - * @parent: parent resource descriptor
> - * @start: resource start address
> - * @n: resource region size
> - * @name: reserving caller's ID string
> - * @flags: IO resource flags
> - */
> -struct resource * __request_region(struct resource *parent,
> +static int __request_region_locked(struct resource *res, struct resource *parent,
>   				   resource_size_t start, resource_size_t n,
>   				   const char *name, int flags)
>   {
>   	DECLARE_WAITQUEUE(wait, current);
> -	struct resource *res = alloc_resource(GFP_KERNEL);
> -	struct resource *orig_parent = parent;
> -
> -	if (!res)
> -		return NULL;
>   
>   	res->name = name;
>   	res->start = start;
>   	res->end = start + n - 1;
>   
> -	write_lock(&resource_lock);
> -
>   	for (;;) {
>   		struct resource *conflict;
>   
> @@ -1241,13 +1226,40 @@ struct resource * __request_region(struct resource *parent,
>   			continue;
>   		}
>   		/* Uhhuh, that didn't work out.. */
> -		free_resource(res);
> -		res = NULL;
> -		break;
> +		return -EBUSY;
>   	}
> +
> +	return 0;
> +}
> +
> +/**
> + * __request_region - create a new busy resource region
> + * @parent: parent resource descriptor
> + * @start: resource start address
> + * @n: resource region size
> + * @name: reserving caller's ID string
> + * @flags: IO resource flags
> + */
> +struct resource *__request_region(struct resource *parent,
> +				  resource_size_t start, resource_size_t n,
> +				  const char *name, int flags)
> +{
> +	struct resource *res = alloc_resource(GFP_KERNEL);
> +	int ret;
> +
> +	if (!res)
> +		return NULL;
> +
> +	write_lock(&resource_lock);
> +	ret = __request_region_locked(res, parent, start, n, name, flags);
>   	write_unlock(&resource_lock);
>   
> -	if (res && orig_parent == &iomem_resource)
> +	if (ret) {
> +		free_resource(res);
> +		return NULL;
> +	}
> +
> +	if (parent == &iomem_resource)
>   		revoke_iomem(res);

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb