Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:
> On Fri, 18 Dec 2015 15:50:24 +0100 Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> 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.
>
This is a nice-to-have addition but it will break at least ACPI
memhotplug: request_resource() has the following:
conflict = request_resource_conflict(root, new);
return conflict ? -EBUSY : 0;
so we'll end up returning -EBUSY from register_memory_resource() and
add_memory(), at the same time acpi_memory_enable_device() counts on
-EEXIST:
result = add_memory(node, info->start_addr, info->length);
/*
* If the memory block has been used by the kernel, add_memory()
* returns -EEXIST. If add_memory() returns the other error, it
* means that this memory block is not used by the kernel.
*/
if (result && result != -EEXIST)
continue;
So I see 3 options here:
1) Keep the overwrite
2) Change the request_resource() return value to -EEXIST
3) Adapt all add_memory() call sites to -EBUSY.
Please let me know your preference.
> --- 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)
> _
--
Vitaly
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