On 08.02.22 02:59, Miaohe Lin wrote:
> Hi:
> On 2022/2/7 22:33, David Hildenbrand wrote:
>> On 07.02.22 14:56, Miaohe Lin wrote:
>>> We can't use kfree() to release the resource as it might come from bootmem.
>>> Use release_mem_region() instead.
>>
>> How can this happen? release_mem_region() is called either from
>> __add_memory() or from add_memory_driver_managed(), where we allocated
>> the region via register_memory_resource(). Both functions shouldn't ever
>> be called before the buddy is up an running.
>>
>> Do you have a backtrace of an actual instance of this issue? Or was this
>> identified as possibly broken by code inspection?
>>
>
> This is identified as possibly broken by code inspection. IIUC, alloc_resource
> is always used to allocate the resource. It has the below logic:
>
> if (bootmem_resource_free) {
> res = bootmem_resource_free;
> bootmem_resource_free = res->sibling;
> }
>
> where bootmem_resource_free is used to reusing the resource entries allocated by boot
> mem after the system is up:
>
> /*
> * For memory hotplug, there is no way to free resource entries allocated
> * by boot mem after the system is up. So for reusing the resource entry
> * we need to remember the resource.
> */
> static struct resource *bootmem_resource_free;
>
> So I think register_memory_resource() can reuse the resource allocated by bootmem.
> Or am I miss anything?
I think you're right, if we did a previous free_resource() of a resource allocated
during boot we could end up reusing that here. My best guess is that this never
really happens.
Wow, that's ugly. It affects essentially anybody reserving+freeing a resource.
E.g., dax/kmem.c similarly does a release_resource(res)+kfree(res)
We could either
a) Expose free_resource() and replace all kfree(res) instances by it
b) Just simplify that. I don't think we care about saving a couple of
bytes in corner cases. I might be wrong (IIRC primarily ppc64 really
succeeds in unplugging boot memory)
diff --git a/kernel/resource.c b/kernel/resource.c
index 9c08d6e9eef2..fe91a72fd951 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -56,14 +56,6 @@ struct resource_constraint {
static DEFINE_RWLOCK(resource_lock);
-/*
- * For memory hotplug, there is no way to free resource entries allocated
- * by boot mem after the system is up. So for reusing the resource entry
- * we need to remember the resource.
- */
-static struct resource *bootmem_resource_free;
-static DEFINE_SPINLOCK(bootmem_resource_lock);
-
static struct resource *next_resource(struct resource *p)
{
if (p->child)
@@ -160,36 +152,19 @@ __initcall(ioresources_init);
static void free_resource(struct resource *res)
{
- if (!res)
- return;
-
- if (!PageSlab(virt_to_head_page(res))) {
- spin_lock(&bootmem_resource_lock);
- res->sibling = bootmem_resource_free;
- bootmem_resource_free = res;
- spin_unlock(&bootmem_resource_lock);
- } else {
+ /*
+ * If the resource was allocated using memblock early during boot
+ * we'll leak it here: we can only return full pages back to the
+ * buddy and trying to be smart and reusing them eventually in
+ * alloc_resource() overcomplicates resource handling.
+ */
+ if (res && PageSlab(virt_to_head_page(res)))
kfree(res);
- }
}
static struct resource *alloc_resource(gfp_t flags)
{
- struct resource *res = NULL;
-
- spin_lock(&bootmem_resource_lock);
- if (bootmem_resource_free) {
- res = bootmem_resource_free;
- bootmem_resource_free = res->sibling;
- }
- spin_unlock(&bootmem_resource_lock);
-
- if (res)
- memset(res, 0, sizeof(struct resource));
- else
- res = kzalloc(sizeof(struct resource), flags);
-
- return res;
+ return kzalloc(sizeof(struct resource), flags);
}
/* Return the conflict entry if you can't request it */
--
Thanks,
David / dhildenb
