linux-kernel - Re: [PATCH v2 2/2] memory-hotplug: keep the request

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Date:	Tue, 12 Jan 2016 15:25:05 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tang Chen <tangchen@...fujitsu.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Dan Williams <dan.j.williams@...el.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Igor Mammedov <imammedo@...hat.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>
Subject: Re: [PATCH v2 2/2] memory-hotplug: keep the request_resource() error
 code

On Mon, 4 Jan 2016, Vitaly Kuznetsov wrote:

> diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
> index 6b0d3ef..e367e4b 100644
> --- a/drivers/acpi/acpi_memhotplug.c
> +++ b/drivers/acpi/acpi_memhotplug.c
> @@ -232,10 +232,10 @@ static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
>  
>  		/*
>  		 * If the memory block has been used by the kernel, add_memory()
> -		 * returns -EEXIST. If add_memory() returns the other error, it
> +		 * returns -EBUSY. If add_memory() returns the other error, it
>  		 * means that this memory block is not used by the kernel.
>  		 */
> -		if (result && result != -EEXIST)
> +		if (result && result != -EBUSY)
>  			continue;
>  
>  		result = acpi_bind_memory_blocks(info, mem_device->device);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 92f9595..07eab2c 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -130,6 +130,7 @@ void mem_hotplug_done(void)
>  static struct resource *register_memory_resource(u64 start, u64 size)
>  {
>  	struct resource *res;
> +	int ret;
>  	res = kzalloc(sizeof(struct resource), GFP_KERNEL);
>  	if (!res)
>  		return ERR_PTR(-ENOMEM);
> @@ -138,10 +139,11 @@ static struct resource *register_memory_resource(u64 start, u64 size)
>  	res->start = start;
>  	res->end = start + size - 1;
>  	res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
> -	if (request_resource(&iomem_resource, res) < 0) {
> +	ret = request_resource(&iomem_resource, res);
> +	if (ret < 0) {
>  		pr_debug("System RAM resource %pR cannot be added\n", res);
>  		kfree(res);
> -		return ERR_PTR(-EEXIST);
> +		return ERR_PTR(ret);
>  	}
>  	return res;
>  }

The result of this change is that add_memory() returns -EBUSY instead of 
-EEXIST for overlapping ranges.  This patch breaks hv_mem_hot_add() since 
it strictly uses a return value of -EEXIST to indicate a non-transient 
failure, so NACK.  It also changes the return value of both the "probe" 
and "dlpar" (on ppc) userspace triggers, which I could imagine is tested 
from existing userspace scripts.