[PATCH] fix __writeback_single_inode WARN_ON

When the inode count is zero in inode writeback, the

	WARN_ON(!(inode->i_state & I_WILL_FREE));

is broken, and needs to test for either I_WILL_FREE|I_FREEING.

When the inode is in I_FREEING state, it's already out of the visibility
of the vm so it can't be freed so it doesn't require the __iget and the
generic_delete_inode path can call the sync internally to the lowlevel
fs callback during the last iput. So the inode being in I_FREEING is
also a valid condition for calling the sync with i_count == 0.

The specific stack trace is this:

  0xc00000007b8fb6e0  0xc00000000010118c  .__writeback_single_inode +0x5c
  0xc00000007b8fb6e0  0xc0000000001014dc (lr) .sync_inode +0x3c
  0xc00000007b8fb790  0xc0000000001014dc  .sync_inode +0x3c
  0xc00000007b8fb820  0xc0000000001a5020  .ext2_sync_inode +0x64
  0xc00000007b8fb8f0  0xc0000000001a65b4  .ext2_truncate +0x3f8
  0xc00000007b8fba40  0xc0000000001a6940  .ext2_delete_inode +0xdc
  0xc00000007b8fbac0  0xc0000000000f7a5c  .generic_delete_inode +0x124
  0xc00000007b8fbb50  0xc0000000000f5fe0  .iput +0xb8
  0xc00000007b8fbbe0  0xc0000000000e9fd4  .sys_unlink +0x2a8
  0xc00000007b8fbd10  0xc00000000001048c  .ret_from_syscall_1 +0x0
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/fs-writeback.c

@@ -247,7 +247,7 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	wait_queue_head_t *wqh;
 
 	if (!atomic_read(&inode->i_count))
-		WARN_ON(!(inode->i_state & I_WILL_FREE));
+		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
 	else
 		WARN_ON(inode->i_state & I_WILL_FREE);