vmcore: continue vmcore initialization if PT_NOTE is found empty

Currently when an empty PT_NOTE is detected, vmcore initialization
fails.  It sounds too harsh.  Because PT_NOTE could be empty, for
example, one offlined a cpu but never restarted kdump service, and after
crash, PT_NOTE program header is there but no data contains.  It's
better to warn about the empty PT_NOTE and continue to initialise
vmcore.

And ultimately the multiple PT_NOTE are merged into a single one, all
empty PT_NOTE are discarded naturally during the merge.  So empty
PT_NOTE is not visible to user space and vmcore is as good as expected.
Signed-off-by: WANG Chao <chaowang@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: Greg Pearson <greg.pearson@hp.com>
Cc: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/vmcore.c

@@ -484,7 +484,6 @@ static int __init update_note_header_size_elf64(const Elf64_Ehdr *ehdr_ptr)
 		phdr_ptr->p_memsz = real_sz;
 		if (real_sz == 0) {
 			pr_warn("Warning: Zero PT_NOTE entries found\n");
-			return -EINVAL;
 		}
 	}
 
@@ -671,7 +670,6 @@ static int __init update_note_header_size_elf32(const Elf32_Ehdr *ehdr_ptr)
 		phdr_ptr->p_memsz = real_sz;
 		if (real_sz == 0) {
 			pr_warn("Warning: Zero PT_NOTE entries found\n");
-			return -EINVAL;
 		}
 	}