[PATCH] remove unsafe BUG_ON()

From: Hugh Dickins <hugh@veritas.com>

PageDirty BUG_ON in __remove_inode_page is, and always has been, unsafe for
SMP or preemption: truncation may be racing against unmapping's
set_page_dirty in zap_pte_range (amongst a few other possibilities).
!PageUptodate error in __set_page_dirty_buffers is unsafe then too.

fs/buffer.c

@@ -822,9 +822,6 @@ int __set_page_dirty_buffers(struct page *page)
 		goto out;
 	}
 
-	if (!PageUptodate(page))
-		buffer_error();
-
 	spin_lock(&mapping->private_lock);
 	if (page_has_buffers(page)) {
 		struct buffer_head *head = page_buffers(page);

mm/filemap.c

@@ -81,8 +81,6 @@ void __remove_from_page_cache(struct page *page)
 {
 	struct address_space *mapping = page->mapping;
 
-	BUG_ON(PageDirty(page) && !PageSwapCache(page));
-
 	radix_tree_delete(&mapping->page_tree, page->index);
 	list_del(&page->list);
 	page->mapping = NULL;