mm: make read_cache_page synchronous

Ensure pages are uptodate after returning from read_cache_page, which allows
us to cut out most of the filesystem-internal PageUptodate calls.

I didn't have a great look down the call chains, but this appears to fixes 7
possible use-before uptodate in hfs, 2 in hfsplus, 1 in jfs, a few in
ecryptfs, 1 in jffs2, and a possible cleared data overwritten with readpage in
block2mtd.  All depending on whether the filler is async and/or can return
with a !uptodate page.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/namei.c

@@ -2671,19 +2671,9 @@ static char *page_getlink(struct dentry * dentry, struct page **ppage)
 	struct address_space *mapping = dentry->d_inode->i_mapping;
 	page = read_mapping_page(mapping, 0, NULL);
 	if (IS_ERR(page))
-		goto sync_fail;
-	wait_on_page_locked(page);
-	if (!PageUptodate(page))
-		goto async_fail;
+		return (char*)page;
 	*ppage = page;
 	return kmap(page);
-
-async_fail:
-	page_cache_release(page);
-	return ERR_PTR(-EIO);
-
-sync_fail:
-	return (char*)page;
 }
 
 int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)