[PATCH] x86_64: Fix change_page_attr cache flushing

Noticed by Terence Ripperda

Undo wrong change in global_flush_tlb. We need to flush the caches in all
cases, not just when pages were reverted. This was a bogus optimization
added earlier, but it was wrong.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/mm/pageattr.c

@@ -220,8 +220,6 @@ void global_flush_tlb(void)
 	down_read(&init_mm.mmap_sem);
 	df = xchg(&df_list, NULL);
 	up_read(&init_mm.mmap_sem);
-	if (!df)
-		return;
 	flush_map((df && !df->next) ? df->address : 0);
 	for (; df; df = next_df) { 
 		next_df = df->next;