svcrdma: avoid duplicate dma unmapping during error recovery

In rdma_read_chunk_frmr() when ib_post_send() fails, the error code path
invokes ib_dma_unmap_sg() to unmap the sg list. It then invokes
svc_rdma_put_frmr() which in turn tries to unmap the same sg list through
ib_dma_unmap_sg() again. This second unmap is invalid and could lead to
problems when the iova being unmapped is subsequently reused. Remove
the call to unmap in rdma_read_chunk_frmr() and let svc_rdma_put_frmr()
handle it.

Fixes: 412a15c0fe ("svcrdma: Port to new memory registration API")
Cc: stable@vger.kernel.org
Signed-off-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/xprtrdma/svc_rdma_recvfrom.c

@@ -347,8 +347,6 @@ int rdma_read_chunk_frmr(struct svcxprt_rdma *xprt,
 	atomic_inc(&rdma_stat_read);
 	return ret;
  err:
-	ib_dma_unmap_sg(xprt->sc_cm_id->device,
-			frmr->sg, frmr->sg_nents, frmr->direction);
 	svc_rdma_put_context(ctxt, 0);
 	svc_rdma_put_frmr(xprt, frmr);
 	return ret;