kernel/resource: fix kfree() of bootmem memory again

Since commit ebff7d8 ("mem hotunplug: fix kfree() of bootmem
memory"), we could get a resource allocated during boot via
alloc_resource().  And it's required to release the resource using
free_resource().  Howerver, many people use kfree directly which will
result in kernel BUG.  In order to fix this without fixing every call
site, just leak a couple of bytes in such corner case.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: ebff7d8 ("mem hotunplug: fix kfree() of bootmem memory")
Signed-off-by: Miaohe Lin <[email protected]>
Suggested-by: David Hildenbrand <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Alistair Popple <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: MiaoheLin

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 */