kmap leak fix for x86_32 kdump

copy_oldmem_page should not return leaving a page frame from the
previous kernel mapped.
Signed-off-by: Fernando Luis Vázquez Cao <fernando@oss.ntt.co.jp>
Acked-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/kernel/crash_dump_32.c

@@ -47,6 +47,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 		if (!kdump_buf_page) {
 			printk(KERN_WARNING "Kdump: Kdump buffer page not"
 				" allocated\n");
+			kunmap_atomic(vaddr, KM_PTE0);
 			return -EFAULT;
 		}
 		copy_page(kdump_buf_page, vaddr);