svcrdma: Move destroy to kernel thread

Some providers may wait while destroying adapter resources.
Since it is possible that the last reference is put on the
dto_tasklet, the actual destroy must be scheduled as a work item.
Signed-off-by: Tom Tucker <tom@opengridcomputing.com>

include/linux/sunrpc/svc_rdma.h

@@ -124,6 +124,7 @@ struct svcxprt_rdma {
 	struct list_head     sc_dto_q;		/* DTO tasklet I/O pending Q */
 	struct list_head     sc_read_complete_q;
 	spinlock_t           sc_read_complete_lock;
+	struct work_struct   sc_work;
 };
 /* sc_flags */
 #define RDMAXPRT_RQ_PENDING	1

net/sunrpc/xprtrdma/svc_rdma_transport.c

@@ -963,12 +963,15 @@ static void svc_rdma_detach(struct svc_xprt *xprt)
 	rdma_destroy_id(rdma->sc_cm_id);
 }
 
-static void svc_rdma_free(struct svc_xprt *xprt)
+static void __svc_rdma_free(struct work_struct *work)
 {
-	struct svcxprt_rdma *rdma = (struct svcxprt_rdma *)xprt;
+	struct svcxprt_rdma *rdma =
+		container_of(work, struct svcxprt_rdma, sc_work);
 	dprintk("svcrdma: svc_rdma_free(%p)\n", rdma);
+
 	/* We should only be called from kref_put */
-	BUG_ON(atomic_read(&xprt->xpt_ref.refcount) != 0);
+	BUG_ON(atomic_read(&rdma->sc_xprt.xpt_ref.refcount) != 0);
+
 	if (rdma->sc_sq_cq && !IS_ERR(rdma->sc_sq_cq))
 		ib_destroy_cq(rdma->sc_sq_cq);
 
@@ -985,6 +988,14 @@ static void svc_rdma_free(struct svc_xprt *xprt)
 	kfree(rdma);
 }
 
+static void svc_rdma_free(struct svc_xprt *xprt)
+{
+	struct svcxprt_rdma *rdma =
+		container_of(xprt, struct svcxprt_rdma, sc_xprt);
+	INIT_WORK(&rdma->sc_work, __svc_rdma_free);
+	schedule_work(&rdma->sc_work);
+}
+
 static int svc_rdma_has_wspace(struct svc_xprt *xprt)
 {
 	struct svcxprt_rdma *rdma =