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Date: Fri, 18 Dec 2015 14:50:22 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Tang Chen <tangchen@cn.fujitsu.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Xishi Qiu <qiuxishi@huawei.com>, Sheng Yong <shengyong1@huawei.com>,
        David Rientjes <rientjes@google.com>,
        Zhu Guihua <zhugh.fnst@cn.fujitsu.com>,
        Dan Williams <dan.j.williams@intel.com>,
        David Vrabel <david.vrabel@citrix.com>,
        Igor Mammedov <imammedo@redhat.com>
Subject: Re: [PATCH] memory-hotplug: don't BUG() in
 register_memory_resource()
Message-Id: <20151218145022.eae1e368c82f090900582fcc@linux-foundation.org>
In-Reply-To: <1450450224-18515-1-git-send-email-vkuznets@redhat.com>
References: <1450450224-18515-1-git-send-email-vkuznets@redhat.com>
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On Fri, 18 Dec 2015 15:50:24 +0100 Vitaly Kuznetsov <vkuznets@redhat.com> wrote:

> Out of memory condition is not a bug and while we can't add new memory in
> such case crashing the system seems wrong. Propagating the return value
> from register_memory_resource() requires interface change.
> 
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> +static int register_memory_resource(u64 start, u64 size,
> +				    struct resource **resource)
>  {
>  	struct resource *res;
>  	res = kzalloc(sizeof(struct resource), GFP_KERNEL);
> -	BUG_ON(!res);
> +	if (!res)
> +		return -ENOMEM;
>  
>  	res->name = "System RAM";
>  	res->start = start;
> @@ -140,9 +142,10 @@ static struct resource *register_memory_resource(u64 start, u64 size)
>  	if (request_resource(&iomem_resource, res) < 0) {
>  		pr_debug("System RAM resource %pR cannot be added\n", res);
>  		kfree(res);
> -		res = NULL;
> +		return -EEXIST;
>  	}
> -	return res;
> +	*resource = res;
> +	return 0;
>  }

Was there a reason for overwriting the request_resource() return value?
Ordinarily it should be propagated back to callers.

Please review.

--- a/mm/memory_hotplug.c~memory-hotplug-dont-bug-in-register_memory_resource-fix
+++ a/mm/memory_hotplug.c
@@ -131,7 +131,9 @@ static int register_memory_resource(u64
 				    struct resource **resource)
 {
 	struct resource *res;
+	int ret = 0;
 	res = kzalloc(sizeof(struct resource), GFP_KERNEL);
+
 	if (!res)
 		return -ENOMEM;
 
@@ -139,13 +141,14 @@ static int register_memory_resource(u64
 	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 -EEXIST;
+	} else {
+		*resource = res;
 	}
-	*resource = res;
-	return 0;
+	return ret;
 }
 
 static void release_memory_resource(struct resource *res)
_