net/rds: Wait for the FRMR_IS_FREE (or FRMR_IS_STALE) transition after posting IB_WR_LOCAL_INV

In order to:
1) avoid a silly bouncing between "clean_list" and "drop_list"
   triggered by function "rds_ib_reg_frmr" as it is releases frmr
   regions whose state is not "FRMR_IS_FREE" right away.

2) prevent an invalid access error in a race from a pending
   "IB_WR_LOCAL_INV" operation with a teardown ("dma_unmap_sg", "put_page")
   and de-registration ("ib_dereg_mr") of the corresponding
   memory region.

Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rds/ib_mr.h

@@ -58,6 +58,8 @@ struct rds_ib_frmr {
 	enum rds_ib_fr_state	fr_state;
 	bool			fr_inv;
 	wait_queue_head_t	fr_inv_done;
+	bool			fr_reg;
+	wait_queue_head_t	fr_reg_done;
 	struct ib_send_wr	fr_wr;
 	unsigned int		dma_npages;
 	unsigned int		sg_byte_len;