tlb_uv.c: Add missing return value check to prevent nptr dereference.

Function init_per_cpu() defined in arch/x86/platform/uv/tlb_uv.c calls kzalloc() to allocate memory for variable uvhub_mask which is used in function get_cpu_topology() and function summarize_uvhub_sockets() later. However, none of the 3 functions mentioned above checks whether uvhub_mask is NULL. As kzalloc() may return NULL, when get_cpu_topology() and summarize_uvhub_sockets() tries to dereference this pointer, it may cause NULL pointer dereference bug.

arch/x86/platform/uv/tlb_uv.c

@@ -2147,6 +2147,9 @@ static int __init init_per_cpu(int nuvhubs, int base_part_pnode)
 	memset(uvhub_descs, 0, nuvhubs * sizeof(struct uvhub_desc));
 	uvhub_mask = kzalloc((nuvhubs+7)/8, GFP_KERNEL);
 
+	if (!uvhub_mask)
+		goto fail;
+
 	if (get_cpu_topology(base_part_pnode, uvhub_descs, uvhub_mask))
 		goto fail;