powerpc/vmemmap: Fix memory leak with vmemmap list allocation failures.

If we fail to allocate vmemmap list, we don't keep track of allocated
vmemmap block buf. Hence on section deactivate we skip vmemmap block
buf free. This results in memory leak.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200731113500.248306-1-aneesh.kumar@linux.ibm.com

arch/powerpc/mm/init_64.c

@@ -162,16 +162,16 @@ static __meminit struct vmemmap_backing * vmemmap_list_alloc(int node)
 	return next++;
 }
 
-static __meminit void vmemmap_list_populate(unsigned long phys,
-					    unsigned long start,
-					    int node)
+static __meminit int vmemmap_list_populate(unsigned long phys,
+					   unsigned long start,
+					   int node)
 {
 	struct vmemmap_backing *vmem_back;
 
 	vmem_back = vmemmap_list_alloc(node);
 	if (unlikely(!vmem_back)) {
-		WARN_ON(1);
-		return;
+		pr_debug("vmemap list allocation failed\n");
+		return -ENOMEM;
 	}
 
 	vmem_back->phys = phys;
@@ -179,6 +179,7 @@ static __meminit void vmemmap_list_populate(unsigned long phys,
 	vmem_back->list = vmemmap_list;
 
 	vmemmap_list = vmem_back;
+	return 0;
 }
 
 static bool altmap_cross_boundary(struct vmem_altmap *altmap, unsigned long start,
@@ -199,6 +200,7 @@ static bool altmap_cross_boundary(struct vmem_altmap *altmap, unsigned long star
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 		struct vmem_altmap *altmap)
 {
+	bool altmap_alloc;
 	unsigned long page_size = 1 << mmu_psize_defs[mmu_vmemmap_psize].shift;
 
 	/* Align to the page size of the linear mapping. */
@@ -228,13 +230,32 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 			p = vmemmap_alloc_block_buf(page_size, node, altmap);
 			if (!p)
 				pr_debug("altmap block allocation failed, falling back to system memory");
+			else
+				altmap_alloc = true;
 		}
-		if (!p)
+		if (!p) {
 			p = vmemmap_alloc_block_buf(page_size, node, NULL);
+			altmap_alloc = false;
+		}
 		if (!p)
 			return -ENOMEM;
 
-		vmemmap_list_populate(__pa(p), start, node);
+		if (vmemmap_list_populate(__pa(p), start, node)) {
+			/*
+			 * If we don't populate vmemap list, we don't have
+			 * the ability to free the allocated vmemmap
+			 * pages in section_deactivate. Hence free them
+			 * here.
+			 */
+			int nr_pfns = page_size >> PAGE_SHIFT;
+			unsigned long page_order = get_order(page_size);
+
+			if (altmap_alloc)
+				vmem_altmap_free(altmap, nr_pfns);
+			else
+				free_pages((unsigned long)p, page_order);
+			return -ENOMEM;
+		}
 
 		pr_debug("      * %016lx..%016lx allocated at %p\n",
 			 start, start + page_size, p);