On Wed, 10 Apr 2013 11:17:00 -0600 Toshi Kani <toshi.kani@xxxxxx> wrote:
> Added release_mem_region_adjustable(), which releases a requested
> region from a currently busy memory resource. This interface
> adjusts the matched memory resource accordingly even if the
> requested region does not match exactly but still fits into.
>
> This new interface is intended for memory hot-delete. During
> bootup, memory resources are inserted from the boot descriptor
> table, such as EFI Memory Table and e820. Each memory resource
> entry usually covers the whole contigous memory range. Memory
> hot-delete request, on the other hand, may target to a particular
> range of memory resource, and its size can be much smaller than
> the whole contiguous memory. Since the existing release interfaces
> like __release_region() require a requested region to be exactly
> matched to a resource entry, they do not allow a partial resource
> to be released.
>
> This new interface is restrictive (i.e. release under certain
> conditions), which is consistent with other release interfaces,
> __release_region() and __release_resource(). Additional release
> conditions, such as an overlapping region to a resource entry,
> can be supported after they are confirmed as valid cases.
>
> There is no change to the existing interfaces since their restriction
> is valid for I/O resources.
>
> ...
>
> +int release_mem_region_adjustable(struct resource *parent,
> + resource_size_t start, resource_size_t size)
> +{
> + struct resource **p;
> + struct resource *res, *new;
> + resource_size_t end;
> + int ret = -EINVAL;
> +
> + end = start + size - 1;
> + if ((start < parent->start) || (end > parent->end))
> + return ret;
> +
> + p = &parent->child;
> + write_lock(&resource_lock);
> +
> + while ((res = *p)) {
> + if (res->start >= end)
> + break;
> +
> + /* look for the next resource if it does not fit into */
> + if (res->start > start || res->end < end) {
> + p = &res->sibling;
> + continue;
> + }
> +
> + if (!(res->flags & IORESOURCE_MEM))
> + break;
> +
> + if (!(res->flags & IORESOURCE_BUSY)) {
> + p = &res->child;
> + continue;
> + }
> +
> + /* found the target resource; let's adjust accordingly */
> + if (res->start == start && res->end == end) {
> + /* free the whole entry */
> + *p = res->sibling;
> + kfree(res);
> + ret = 0;
> + } else if (res->start == start && res->end != end) {
> + /* adjust the start */
> + ret = __adjust_resource(res, end + 1,
> + res->end - end);
> + } else if (res->start != start && res->end == end) {
> + /* adjust the end */
> + ret = __adjust_resource(res, res->start,
> + start - res->start);
> + } else {
> + /* split into two entries */
> + new = kzalloc(sizeof(struct resource), GFP_KERNEL);
Nope, we can't perform a GFP_KERNEL allocation under write_lock().
Was this code path runtime tested? If no, please try
to find a way to test it. If yes, please see
Documentation/SubmitChecklist section 12 and use that in the future.
I'll switch it to GFP_ATOMIC. Which is horridly lame but the
allocation is small and alternatives are unobvious.
> + if (!new) {
> + ret = -ENOMEM;
> + break;
> + }
> + new->name = res->name;
> + new->start = end + 1;
> + new->end = res->end;
> + new->flags = res->flags;
> + new->parent = res->parent;
> + new->sibling = res->sibling;
> + new->child = NULL;
> +
> + ret = __adjust_resource(res, res->start,
> + start - res->start);
> + if (ret) {
> + kfree(new);
> + break;
> + }
> + res->sibling = new;
> + }
> +
> + break;
> + }
> +
> + write_unlock(&resource_lock);
> + return ret;
> +}
> +#endif /* CONFIG_MEMORY_HOTPLUG */
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