vfs: Revert spurious fix to spinning prevention in prune_icache_sb

Revert commit 62a3ddef6181 ("vfs: fix spinning prevention in prune_icache_sb").

This commit doesn't look right: since we are looking at the tail of the
list (sb->s_inode_lru.prev) if we want to skip an inode, we should put
it back at the head of the list instead of the tail, otherwise we will
keep spinning on it.

Discovered when investigating why prune_icache_sb came top in perf
reports of a swapping load.

Signed-off-by: Suleiman Souhlal <suleiman@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: stable@vger.kernel.org # v3.2+
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/inode.c

@@ -725,7 +725,7 @@ void prune_icache_sb(struct super_block *sb, int nr_to_scan)
 		 * inode to the back of the list so we don't spin on it.
 		 */
 		if (!spin_trylock(&inode->i_lock)) {
-			list_move_tail(&inode->i_lru, &sb->s_inode_lru);
+			list_move(&inode->i_lru, &sb->s_inode_lru);
 			continue;
 		}