net/sunrpc/xprtrdma/frwr_ops.c - kernel/bruno - Git at Google

 /*
  * Copyright (c) 2015 Oracle.  All rights reserved.
  * Copyright (c) 2003-2007 Network Appliance, Inc. All rights reserved.
  */

 /* Lightweight memory registration using Fast Registration Work
  * Requests (FRWR). Also referred to sometimes as FRMR mode.
  *
  * FRWR features ordered asynchronous registration and deregistration
  * of arbitrarily sized memory regions. This is the fastest and safest
  * but most complex memory registration mode.
  */

 /* Normal operation
  *
  * A Memory Region is prepared for RDMA READ or WRITE using a FAST_REG
  * Work Request (frmr_op_map). When the RDMA operation is finished, this
  * Memory Region is invalidated using a LOCAL_INV Work Request
  * (frmr_op_unmap).
  *
  * Typically these Work Requests are not signaled, and neither are RDMA
  * SEND Work Requests (with the exception of signaling occasionally to
  * prevent provider work queue overflows). This greatly reduces HCA
  * interrupt workload.
  *
  * As an optimization, frwr_op_unmap marks MRs INVALID before the
  * LOCAL_INV WR is posted. If posting succeeds, the MR is placed on
  * rb_mws immediately so that no work (like managing a linked list
  * under a spinlock) is needed in the completion upcall.
  *
  * But this means that frwr_op_map() can occasionally encounter an MR
  * that is INVALID but the LOCAL_INV WR has not completed. Work Queue
  * ordering prevents a subsequent FAST_REG WR from executing against
  * that MR while it is still being invalidated.
  */

 /* Transport recovery
  *
  * ->op_map and the transport connect worker cannot run at the same
  * time, but ->op_unmap can fire while the transport connect worker
  * is running. Thus MR recovery is handled in ->op_map, to guarantee
  * that recovered MRs are owned by a sending RPC, and not one where
  * ->op_unmap could fire at the same time transport reconnect is
  * being done.
  *
  * When the underlying transport disconnects, MRs are left in one of
  * three states:
  *
  * INVALID:	The MR was not in use before the QP entered ERROR state.
  *		(Or, the LOCAL_INV WR has not completed or flushed yet).
  *
  * STALE:	The MR was being registered or unregistered when the QP
  *		entered ERROR state, and the pending WR was flushed.
  *
  * VALID:	The MR was registered before the QP entered ERROR state.
  *
  * When frwr_op_map encounters STALE and VALID MRs, they are recovered
  * with ib_dereg_mr and then are re-initialized. Beause MR recovery
  * allocates fresh resources, it is deferred to a workqueue, and the
  * recovered MRs are placed back on the rb_mws list when recovery is
  * complete. frwr_op_map allocates another MR for the current RPC while
  * the broken MR is reset.
  *
  * To ensure that frwr_op_map doesn't encounter an MR that is marked
  * INVALID but that is about to be flushed due to a previous transport
  * disconnect, the transport connect worker attempts to drain all
  * pending send queue WRs before the transport is reconnected.
  */

 #include "xprt_rdma.h"

 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 # define RPCDBG_FACILITY	RPCDBG_TRANS
 #endif

 static struct workqueue_struct *frwr_recovery_wq;

 #define FRWR_RECOVERY_WQ_FLAGS		(WQ_UNBOUND | WQ_MEM_RECLAIM)

 int
 frwr_alloc_recovery_wq(void)
 {
 	frwr_recovery_wq = alloc_workqueue("frwr_recovery",
 					   FRWR_RECOVERY_WQ_FLAGS, 0);
 	return !frwr_recovery_wq ? -ENOMEM : 0;
 }

 void
 frwr_destroy_recovery_wq(void)
 {
 	struct workqueue_struct *wq;

 	if (!frwr_recovery_wq)
 		return;

 	wq = frwr_recovery_wq;
 	frwr_recovery_wq = NULL;
 	destroy_workqueue(wq);
 }

 /* Deferred reset of a single FRMR. Generate a fresh rkey by
  * replacing the MR.
  *
  * There's no recovery if this fails. The FRMR is abandoned, but
  * remains in rb_all. It will be cleaned up when the transport is
  * destroyed.
  */
 static void
 __frwr_recovery_worker(struct work_struct *work)
 {
 	struct rpcrdma_mw *r = container_of(work, struct rpcrdma_mw,
 					    r.frmr.fr_work);
 	struct rpcrdma_xprt *r_xprt = r->r.frmr.fr_xprt;
 	unsigned int depth = r_xprt->rx_ia.ri_max_frmr_depth;
 	struct ib_pd *pd = r_xprt->rx_ia.ri_pd;

 	if (ib_dereg_mr(r->r.frmr.fr_mr))
 		goto out_fail;

 	r->r.frmr.fr_mr = ib_alloc_mr(pd, IB_MR_TYPE_MEM_REG, depth);
 	if (IS_ERR(r->r.frmr.fr_mr))
 		goto out_fail;

 	dprintk("RPC:       %s: recovered FRMR %p\n", __func__, r);
 	r->r.frmr.fr_state = FRMR_IS_INVALID;
 	rpcrdma_put_mw(r_xprt, r);
 	return;

 out_fail:
 	pr_warn("RPC:       %s: FRMR %p unrecovered\n",
 		__func__, r);
 }

 /* A broken MR was discovered in a context that can't sleep.
  * Defer recovery to the recovery worker.
  */
 static void
 __frwr_queue_recovery(struct rpcrdma_mw *r)
 {
 	INIT_WORK(&r->r.frmr.fr_work, __frwr_recovery_worker);
 	queue_work(frwr_recovery_wq, &r->r.frmr.fr_work);
 }

 static int
 __frwr_init(struct rpcrdma_mw *r, struct ib_pd *pd, struct ib_device *device,
 	    unsigned int depth)
 {
 	struct rpcrdma_frmr *f = &r->r.frmr;
 	int rc;

 	f->fr_mr = ib_alloc_mr(pd, IB_MR_TYPE_MEM_REG, depth);
 	if (IS_ERR(f->fr_mr))
 		goto out_mr_err;

 	f->sg = kcalloc(depth, sizeof(*f->sg), GFP_KERNEL);
 	if (!f->sg)
 		goto out_list_err;

 	sg_init_table(f->sg, depth);

 	return 0;

 out_mr_err:
 	rc = PTR_ERR(f->fr_mr);
 	dprintk("RPC:       %s: ib_alloc_mr status %i\n",
 		__func__, rc);
 	return rc;

 out_list_err:
 	rc = -ENOMEM;
 	dprintk("RPC:       %s: sg allocation failure\n",
 		__func__);
 	ib_dereg_mr(f->fr_mr);
 	return rc;
 }

 static void
 __frwr_release(struct rpcrdma_mw *r)
 {
 	int rc;

 	rc = ib_dereg_mr(r->r.frmr.fr_mr);
 	if (rc)
 		dprintk("RPC:       %s: ib_dereg_mr status %i\n",
 			__func__, rc);
 	kfree(r->r.frmr.sg);
 }

 static int
 frwr_op_open(struct rpcrdma_ia *ia, struct rpcrdma_ep *ep,
 	     struct rpcrdma_create_data_internal *cdata)
 {
 	struct ib_device_attr *devattr = &ia->ri_devattr;
 	int depth, delta;

 	ia->ri_max_frmr_depth =
 			min_t(unsigned int, RPCRDMA_MAX_DATA_SEGS,
 			      devattr->max_fast_reg_page_list_len);
 	dprintk("RPC:       %s: device's max FR page list len = %u\n",
 		__func__, ia->ri_max_frmr_depth);

 	/* Add room for frmr register and invalidate WRs.
 	 * 1. FRMR reg WR for head
 	 * 2. FRMR invalidate WR for head
 	 * 3. N FRMR reg WRs for pagelist
 	 * 4. N FRMR invalidate WRs for pagelist
 	 * 5. FRMR reg WR for tail
 	 * 6. FRMR invalidate WR for tail
 	 * 7. The RDMA_SEND WR
 	 */
 	depth = 7;

 	/* Calculate N if the device max FRMR depth is smaller than
 	 * RPCRDMA_MAX_DATA_SEGS.
 	 */
 	if (ia->ri_max_frmr_depth < RPCRDMA_MAX_DATA_SEGS) {
 		delta = RPCRDMA_MAX_DATA_SEGS - ia->ri_max_frmr_depth;
 		do {
 			depth += 2; /* FRMR reg + invalidate */
 			delta -= ia->ri_max_frmr_depth;
 		} while (delta > 0);
 	}

 	ep->rep_attr.cap.max_send_wr *= depth;
 	if (ep->rep_attr.cap.max_send_wr > devattr->max_qp_wr) {
 		cdata->max_requests = devattr->max_qp_wr / depth;
 		if (!cdata->max_requests)
 			return -EINVAL;
 		ep->rep_attr.cap.max_send_wr = cdata->max_requests *
 					       depth;
 	}

 	return 0;
 }

 /* FRWR mode conveys a list of pages per chunk segment. The
  * maximum length of that list is the FRWR page list depth.
  */
 static size_t
 frwr_op_maxpages(struct rpcrdma_xprt *r_xprt)
 {
 	struct rpcrdma_ia *ia = &r_xprt->rx_ia;

 	return min_t(unsigned int, RPCRDMA_MAX_DATA_SEGS,
 		     rpcrdma_max_segments(r_xprt) * ia->ri_max_frmr_depth);
 }

 /* If FAST_REG or LOCAL_INV failed, indicate the frmr needs to be reset. */
 static void
 frwr_sendcompletion(struct ib_wc *wc)
 {
 	struct rpcrdma_mw *r;

 	if (likely(wc->status == IB_WC_SUCCESS))
 		return;

 	/* WARNING: Only wr_id and status are reliable at this point */
 	r = (struct rpcrdma_mw *)(unsigned long)wc->wr_id;
 	if (wc->status == IB_WC_WR_FLUSH_ERR)
 		dprintk("RPC:       %s: frmr %p flushed\n", __func__, r);
 	else
 		pr_warn("RPC:       %s: frmr %p error, status %s (%d)\n",
 			__func__, r, ib_wc_status_msg(wc->status), wc->status);
 	r->r.frmr.fr_state = FRMR_IS_STALE;
 }

 static int
 frwr_op_init(struct rpcrdma_xprt *r_xprt)
 {
 	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
 	struct ib_device *device = r_xprt->rx_ia.ri_device;
 	unsigned int depth = r_xprt->rx_ia.ri_max_frmr_depth;
 	struct ib_pd *pd = r_xprt->rx_ia.ri_pd;
 	int i;

 	spin_lock_init(&buf->rb_mwlock);
 	INIT_LIST_HEAD(&buf->rb_mws);
 	INIT_LIST_HEAD(&buf->rb_all);

 	i = max_t(int, RPCRDMA_MAX_DATA_SEGS / depth, 1);
 	i += 2;				/* head + tail */
 	i *= buf->rb_max_requests;	/* one set for each RPC slot */
 	dprintk("RPC:       %s: initalizing %d FRMRs\n", __func__, i);

 	while (i--) {
 		struct rpcrdma_mw *r;
 		int rc;

 		r = kzalloc(sizeof(*r), GFP_KERNEL);
 		if (!r)
 			return -ENOMEM;

 		rc = __frwr_init(r, pd, device, depth);
 		if (rc) {
 			kfree(r);
 			return rc;
 		}

 		list_add(&r->mw_list, &buf->rb_mws);
 		list_add(&r->mw_all, &buf->rb_all);
 		r->mw_sendcompletion = frwr_sendcompletion;
 		r->r.frmr.fr_xprt = r_xprt;
 	}

 	return 0;
 }

 /* Post a FAST_REG Work Request to register a memory region
  * for remote access via RDMA READ or RDMA WRITE.
  */
 static int
 frwr_op_map(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg,
 	    int nsegs, bool writing)
 {
 	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
 	struct ib_device *device = ia->ri_device;
 	enum dma_data_direction direction = rpcrdma_data_dir(writing);
 	struct rpcrdma_mr_seg *seg1 = seg;
 	struct rpcrdma_mw *mw;
 	struct rpcrdma_frmr *frmr;
 	struct ib_mr *mr;
 	struct ib_reg_wr reg_wr;
 	struct ib_send_wr *bad_wr;
 	int rc, i, n, dma_nents;
 	u8 key;

 	mw = seg1->rl_mw;
 	seg1->rl_mw = NULL;
 	do {
 		if (mw)
 			__frwr_queue_recovery(mw);
 		mw = rpcrdma_get_mw(r_xprt);
 		if (!mw)
 			return -ENOMEM;
 	} while (mw->r.frmr.fr_state != FRMR_IS_INVALID);
 	frmr = &mw->r.frmr;
 	frmr->fr_state = FRMR_IS_VALID;
 	mr = frmr->fr_mr;

 	if (nsegs > ia->ri_max_frmr_depth)
 		nsegs = ia->ri_max_frmr_depth;

 	for (i = 0; i < nsegs;) {
 		if (seg->mr_page)
 			sg_set_page(&frmr->sg[i],
 				    seg->mr_page,
 				    seg->mr_len,
 				    offset_in_page(seg->mr_offset));
 		else
 			sg_set_buf(&frmr->sg[i], seg->mr_offset,
 				   seg->mr_len);

 		++seg;
 		++i;

 		/* Check for holes */
 		if ((i < nsegs && offset_in_page(seg->mr_offset)) ||
 		    offset_in_page((seg-1)->mr_offset + (seg-1)->mr_len))
 			break;
 	}
 	frmr->sg_nents = i;

 	dma_nents = ib_dma_map_sg(device, frmr->sg, frmr->sg_nents, direction);
 	if (!dma_nents) {
 		pr_err("RPC:       %s: failed to dma map sg %p sg_nents %u\n",
 		       __func__, frmr->sg, frmr->sg_nents);
 		return -ENOMEM;
 	}

 	n = ib_map_mr_sg(mr, frmr->sg, frmr->sg_nents, PAGE_SIZE);
 	if (unlikely(n != frmr->sg_nents)) {
 		pr_err("RPC:       %s: failed to map mr %p (%u/%u)\n",
 		       __func__, frmr->fr_mr, n, frmr->sg_nents);
 		rc = n < 0 ? n : -EINVAL;
 		goto out_senderr;
 	}

 	dprintk("RPC:       %s: Using frmr %p to map %u segments (%u bytes)\n",
 		__func__, mw, frmr->sg_nents, mr->length);

 	key = (u8)(mr->rkey & 0x000000FF);
 	ib_update_fast_reg_key(mr, ++key);

 	reg_wr.wr.next = NULL;
 	reg_wr.wr.opcode = IB_WR_REG_MR;
 	reg_wr.wr.wr_id = (uintptr_t)mw;
 	reg_wr.wr.num_sge = 0;
 	reg_wr.wr.send_flags = 0;
 	reg_wr.mr = mr;
 	reg_wr.key = mr->rkey;
 	reg_wr.access = writing ?
 			IB_ACCESS_REMOTE_WRITE | IB_ACCESS_LOCAL_WRITE :
 			IB_ACCESS_REMOTE_READ;

 	DECR_CQCOUNT(&r_xprt->rx_ep);
 	rc = ib_post_send(ia->ri_id->qp, &reg_wr.wr, &bad_wr);
 	if (rc)
 		goto out_senderr;

 	seg1->mr_dir = direction;
 	seg1->rl_mw = mw;
 	seg1->mr_rkey = mr->rkey;
 	seg1->mr_base = mr->iova;
 	seg1->mr_nsegs = frmr->sg_nents;
 	seg1->mr_len = mr->length;

 	return frmr->sg_nents;

 out_senderr:
 	dprintk("RPC:       %s: ib_post_send status %i\n", __func__, rc);
 	ib_dma_unmap_sg(device, frmr->sg, dma_nents, direction);
 	__frwr_queue_recovery(mw);
 	return rc;
 }

 /* Post a LOCAL_INV Work Request to prevent further remote access
  * via RDMA READ or RDMA WRITE.
  */
 static int
 frwr_op_unmap(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg)
 {
 	struct rpcrdma_mr_seg *seg1 = seg;
 	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
 	struct rpcrdma_mw *mw = seg1->rl_mw;
 	struct rpcrdma_frmr *frmr = &mw->r.frmr;
 	struct ib_send_wr invalidate_wr, *bad_wr;
 	int rc, nsegs = seg->mr_nsegs;

 	dprintk("RPC:       %s: FRMR %p\n", __func__, mw);

 	seg1->rl_mw = NULL;
 	frmr->fr_state = FRMR_IS_INVALID;

 	memset(&invalidate_wr, 0, sizeof(invalidate_wr));
 	invalidate_wr.wr_id = (unsigned long)(void *)mw;
 	invalidate_wr.opcode = IB_WR_LOCAL_INV;
 	invalidate_wr.ex.invalidate_rkey = frmr->fr_mr->rkey;
 	DECR_CQCOUNT(&r_xprt->rx_ep);

 	ib_dma_unmap_sg(ia->ri_device, frmr->sg, frmr->sg_nents, seg1->mr_dir);
 	read_lock(&ia->ri_qplock);
 	rc = ib_post_send(ia->ri_id->qp, &invalidate_wr, &bad_wr);
 	read_unlock(&ia->ri_qplock);
 	if (rc)
 		goto out_err;

 	rpcrdma_put_mw(r_xprt, mw);
 	return nsegs;

 out_err:
 	dprintk("RPC:       %s: ib_post_send status %i\n", __func__, rc);
 	__frwr_queue_recovery(mw);
 	return nsegs;
 }

 static void
 frwr_op_destroy(struct rpcrdma_buffer *buf)
 {
 	struct rpcrdma_mw *r;

 	/* Ensure stale MWs for "buf" are no longer in flight */
 	flush_workqueue(frwr_recovery_wq);

 	while (!list_empty(&buf->rb_all)) {
 		r = list_entry(buf->rb_all.next, struct rpcrdma_mw, mw_all);
 		list_del(&r->mw_all);
 		__frwr_release(r);
 		kfree(r);
 	}
 }

 const struct rpcrdma_memreg_ops rpcrdma_frwr_memreg_ops = {
 	.ro_map				= frwr_op_map,
 	.ro_unmap			= frwr_op_unmap,
 	.ro_open			= frwr_op_open,
 	.ro_maxpages			= frwr_op_maxpages,
 	.ro_init			= frwr_op_init,
 	.ro_destroy			= frwr_op_destroy,
 	.ro_displayname			= "frwr",
 };
	/*
	* Copyright (c) 2015 Oracle. All rights reserved.
	* Copyright (c) 2003-2007 Network Appliance, Inc. All rights reserved.
	*/

	/* Lightweight memory registration using Fast Registration Work
	* Requests (FRWR). Also referred to sometimes as FRMR mode.
	*
	* FRWR features ordered asynchronous registration and deregistration
	* of arbitrarily sized memory regions. This is the fastest and safest
	* but most complex memory registration mode.
	*/

	/* Normal operation
	*
	* A Memory Region is prepared for RDMA READ or WRITE using a FAST_REG
	* Work Request (frmr_op_map). When the RDMA operation is finished, this
	* Memory Region is invalidated using a LOCAL_INV Work Request
	* (frmr_op_unmap).
	*
	* Typically these Work Requests are not signaled, and neither are RDMA
	* SEND Work Requests (with the exception of signaling occasionally to
	* prevent provider work queue overflows). This greatly reduces HCA
	* interrupt workload.
	*
	* As an optimization, frwr_op_unmap marks MRs INVALID before the
	* LOCAL_INV WR is posted. If posting succeeds, the MR is placed on
	* rb_mws immediately so that no work (like managing a linked list
	* under a spinlock) is needed in the completion upcall.
	*
	* But this means that frwr_op_map() can occasionally encounter an MR
	* that is INVALID but the LOCAL_INV WR has not completed. Work Queue
	* ordering prevents a subsequent FAST_REG WR from executing against
	* that MR while it is still being invalidated.
	*/

	/* Transport recovery
	*
	* ->op_map and the transport connect worker cannot run at the same
	* time, but ->op_unmap can fire while the transport connect worker
	* is running. Thus MR recovery is handled in ->op_map, to guarantee
	* that recovered MRs are owned by a sending RPC, and not one where
	* ->op_unmap could fire at the same time transport reconnect is
	* being done.
	*
	* When the underlying transport disconnects, MRs are left in one of
	* three states:
	*
	* INVALID: The MR was not in use before the QP entered ERROR state.
	* (Or, the LOCAL_INV WR has not completed or flushed yet).
	*
	* STALE: The MR was being registered or unregistered when the QP
	* entered ERROR state, and the pending WR was flushed.
	*
	* VALID: The MR was registered before the QP entered ERROR state.
	*
	* When frwr_op_map encounters STALE and VALID MRs, they are recovered
	* with ib_dereg_mr and then are re-initialized. Beause MR recovery
	* allocates fresh resources, it is deferred to a workqueue, and the
	* recovered MRs are placed back on the rb_mws list when recovery is
	* complete. frwr_op_map allocates another MR for the current RPC while
	* the broken MR is reset.
	*
	* To ensure that frwr_op_map doesn't encounter an MR that is marked
	* INVALID but that is about to be flushed due to a previous transport
	* disconnect, the transport connect worker attempts to drain all
	* pending send queue WRs before the transport is reconnected.
	*/

	#include "xprt_rdma.h"

	#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
	# define RPCDBG_FACILITY RPCDBG_TRANS
	#endif

	static struct workqueue_struct *frwr_recovery_wq;

	#define FRWR_RECOVERY_WQ_FLAGS (WQ_UNBOUND \| WQ_MEM_RECLAIM)

	int
	frwr_alloc_recovery_wq(void)
	{
	frwr_recovery_wq = alloc_workqueue("frwr_recovery",
	FRWR_RECOVERY_WQ_FLAGS, 0);
	return !frwr_recovery_wq ? -ENOMEM : 0;
	}

	void
	frwr_destroy_recovery_wq(void)
	{
	struct workqueue_struct *wq;

	if (!frwr_recovery_wq)
	return;

	wq = frwr_recovery_wq;
	frwr_recovery_wq = NULL;
	destroy_workqueue(wq);
	}

	/* Deferred reset of a single FRMR. Generate a fresh rkey by
	* replacing the MR.
	*
	* There's no recovery if this fails. The FRMR is abandoned, but
	* remains in rb_all. It will be cleaned up when the transport is
	* destroyed.
	*/
	static void
	__frwr_recovery_worker(struct work_struct *work)
	{
	struct rpcrdma_mw *r = container_of(work, struct rpcrdma_mw,
	r.frmr.fr_work);
	struct rpcrdma_xprt *r_xprt = r->r.frmr.fr_xprt;
	unsigned int depth = r_xprt->rx_ia.ri_max_frmr_depth;
	struct ib_pd *pd = r_xprt->rx_ia.ri_pd;

	if (ib_dereg_mr(r->r.frmr.fr_mr))
	goto out_fail;

	r->r.frmr.fr_mr = ib_alloc_mr(pd, IB_MR_TYPE_MEM_REG, depth);
	if (IS_ERR(r->r.frmr.fr_mr))
	goto out_fail;

	dprintk("RPC: %s: recovered FRMR %p\n", __func__, r);
	r->r.frmr.fr_state = FRMR_IS_INVALID;
	rpcrdma_put_mw(r_xprt, r);
	return;

	out_fail:
	pr_warn("RPC: %s: FRMR %p unrecovered\n",
	__func__, r);
	}

	/* A broken MR was discovered in a context that can't sleep.
	* Defer recovery to the recovery worker.
	*/
	static void
	__frwr_queue_recovery(struct rpcrdma_mw *r)
	{
	INIT_WORK(&r->r.frmr.fr_work, __frwr_recovery_worker);
	queue_work(frwr_recovery_wq, &r->r.frmr.fr_work);
	}

	static int
	__frwr_init(struct rpcrdma_mw r, struct ib_pd pd, struct ib_device *device,
	unsigned int depth)
	{
	struct rpcrdma_frmr *f = &r->r.frmr;
	int rc;

	f->fr_mr = ib_alloc_mr(pd, IB_MR_TYPE_MEM_REG, depth);
	if (IS_ERR(f->fr_mr))
	goto out_mr_err;

	f->sg = kcalloc(depth, sizeof(*f->sg), GFP_KERNEL);
	if (!f->sg)
	goto out_list_err;

	sg_init_table(f->sg, depth);

	return 0;

	out_mr_err:
	rc = PTR_ERR(f->fr_mr);
	dprintk("RPC: %s: ib_alloc_mr status %i\n",
	__func__, rc);
	return rc;

	out_list_err:
	rc = -ENOMEM;
	dprintk("RPC: %s: sg allocation failure\n",
	__func__);
	ib_dereg_mr(f->fr_mr);
	return rc;
	}

	static void
	__frwr_release(struct rpcrdma_mw *r)
	{
	int rc;

	rc = ib_dereg_mr(r->r.frmr.fr_mr);
	if (rc)
	dprintk("RPC: %s: ib_dereg_mr status %i\n",
	__func__, rc);
	kfree(r->r.frmr.sg);
	}

	static int
	frwr_op_open(struct rpcrdma_ia ia, struct rpcrdma_ep ep,
	struct rpcrdma_create_data_internal *cdata)
	{
	struct ib_device_attr *devattr = &ia->ri_devattr;
	int depth, delta;

	ia->ri_max_frmr_depth =
	min_t(unsigned int, RPCRDMA_MAX_DATA_SEGS,
	devattr->max_fast_reg_page_list_len);
	dprintk("RPC: %s: device's max FR page list len = %u\n",
	__func__, ia->ri_max_frmr_depth);

	/* Add room for frmr register and invalidate WRs.
	* 1. FRMR reg WR for head
	* 2. FRMR invalidate WR for head
	* 3. N FRMR reg WRs for pagelist
	* 4. N FRMR invalidate WRs for pagelist
	* 5. FRMR reg WR for tail
	* 6. FRMR invalidate WR for tail
	* 7. The RDMA_SEND WR
	*/
	depth = 7;

	/* Calculate N if the device max FRMR depth is smaller than
	* RPCRDMA_MAX_DATA_SEGS.
	*/
	if (ia->ri_max_frmr_depth < RPCRDMA_MAX_DATA_SEGS) {
	delta = RPCRDMA_MAX_DATA_SEGS - ia->ri_max_frmr_depth;
	do {
	depth += 2; /* FRMR reg + invalidate */
	delta -= ia->ri_max_frmr_depth;
	} while (delta > 0);
	}

	ep->rep_attr.cap.max_send_wr *= depth;
	if (ep->rep_attr.cap.max_send_wr > devattr->max_qp_wr) {
	cdata->max_requests = devattr->max_qp_wr / depth;
	if (!cdata->max_requests)
	return -EINVAL;
	ep->rep_attr.cap.max_send_wr = cdata->max_requests *
	depth;
	}

	return 0;
	}

	/* FRWR mode conveys a list of pages per chunk segment. The
	* maximum length of that list is the FRWR page list depth.
	*/
	static size_t
	frwr_op_maxpages(struct rpcrdma_xprt *r_xprt)
	{
	struct rpcrdma_ia *ia = &r_xprt->rx_ia;

	return min_t(unsigned int, RPCRDMA_MAX_DATA_SEGS,
	rpcrdma_max_segments(r_xprt) * ia->ri_max_frmr_depth);
	}

	/* If FAST_REG or LOCAL_INV failed, indicate the frmr needs to be reset. */
	static void
	frwr_sendcompletion(struct ib_wc *wc)
	{
	struct rpcrdma_mw *r;

	if (likely(wc->status == IB_WC_SUCCESS))
	return;

	/* WARNING: Only wr_id and status are reliable at this point */
	r = (struct rpcrdma_mw *)(unsigned long)wc->wr_id;
	if (wc->status == IB_WC_WR_FLUSH_ERR)
	dprintk("RPC: %s: frmr %p flushed\n", __func__, r);
	else
	pr_warn("RPC: %s: frmr %p error, status %s (%d)\n",
	__func__, r, ib_wc_status_msg(wc->status), wc->status);
	r->r.frmr.fr_state = FRMR_IS_STALE;
	}

	static int
	frwr_op_init(struct rpcrdma_xprt *r_xprt)
	{
	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
	struct ib_device *device = r_xprt->rx_ia.ri_device;
	unsigned int depth = r_xprt->rx_ia.ri_max_frmr_depth;
	struct ib_pd *pd = r_xprt->rx_ia.ri_pd;
	int i;

	spin_lock_init(&buf->rb_mwlock);
	INIT_LIST_HEAD(&buf->rb_mws);
	INIT_LIST_HEAD(&buf->rb_all);

	i = max_t(int, RPCRDMA_MAX_DATA_SEGS / depth, 1);
	i += 2; /* head + tail */
	i = buf->rb_max_requests; / one set for each RPC slot */
	dprintk("RPC: %s: initalizing %d FRMRs\n", __func__, i);

	while (i--) {
	struct rpcrdma_mw *r;
	int rc;

	r = kzalloc(sizeof(*r), GFP_KERNEL);
	if (!r)
	return -ENOMEM;

	rc = __frwr_init(r, pd, device, depth);
	if (rc) {
	kfree(r);
	return rc;
	}

	list_add(&r->mw_list, &buf->rb_mws);
	list_add(&r->mw_all, &buf->rb_all);
	r->mw_sendcompletion = frwr_sendcompletion;
	r->r.frmr.fr_xprt = r_xprt;
	}

	return 0;
	}

	/* Post a FAST_REG Work Request to register a memory region
	* for remote access via RDMA READ or RDMA WRITE.
	*/
	static int
	frwr_op_map(struct rpcrdma_xprt r_xprt, struct rpcrdma_mr_seg seg,
	int nsegs, bool writing)
	{
	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
	struct ib_device *device = ia->ri_device;
	enum dma_data_direction direction = rpcrdma_data_dir(writing);
	struct rpcrdma_mr_seg *seg1 = seg;
	struct rpcrdma_mw *mw;
	struct rpcrdma_frmr *frmr;
	struct ib_mr *mr;
	struct ib_reg_wr reg_wr;
	struct ib_send_wr *bad_wr;
	int rc, i, n, dma_nents;
	u8 key;

	mw = seg1->rl_mw;
	seg1->rl_mw = NULL;
	do {
	if (mw)
	__frwr_queue_recovery(mw);
	mw = rpcrdma_get_mw(r_xprt);
	if (!mw)
	return -ENOMEM;
	} while (mw->r.frmr.fr_state != FRMR_IS_INVALID);
	frmr = &mw->r.frmr;
	frmr->fr_state = FRMR_IS_VALID;
	mr = frmr->fr_mr;

	if (nsegs > ia->ri_max_frmr_depth)
	nsegs = ia->ri_max_frmr_depth;

	for (i = 0; i < nsegs;) {
	if (seg->mr_page)
	sg_set_page(&frmr->sg[i],
	seg->mr_page,
	seg->mr_len,
	offset_in_page(seg->mr_offset));
	else
	sg_set_buf(&frmr->sg[i], seg->mr_offset,
	seg->mr_len);

	++seg;
	++i;

	/* Check for holes */
	if ((i < nsegs && offset_in_page(seg->mr_offset)) \|\|
	offset_in_page((seg-1)->mr_offset + (seg-1)->mr_len))
	break;
	}
	frmr->sg_nents = i;

	dma_nents = ib_dma_map_sg(device, frmr->sg, frmr->sg_nents, direction);
	if (!dma_nents) {
	pr_err("RPC: %s: failed to dma map sg %p sg_nents %u\n",
	__func__, frmr->sg, frmr->sg_nents);
	return -ENOMEM;
	}

	n = ib_map_mr_sg(mr, frmr->sg, frmr->sg_nents, PAGE_SIZE);
	if (unlikely(n != frmr->sg_nents)) {
	pr_err("RPC: %s: failed to map mr %p (%u/%u)\n",
	__func__, frmr->fr_mr, n, frmr->sg_nents);
	rc = n < 0 ? n : -EINVAL;
	goto out_senderr;
	}

	dprintk("RPC: %s: Using frmr %p to map %u segments (%u bytes)\n",
	__func__, mw, frmr->sg_nents, mr->length);

	key = (u8)(mr->rkey & 0x000000FF);
	ib_update_fast_reg_key(mr, ++key);

	reg_wr.wr.next = NULL;
	reg_wr.wr.opcode = IB_WR_REG_MR;
	reg_wr.wr.wr_id = (uintptr_t)mw;
	reg_wr.wr.num_sge = 0;
	reg_wr.wr.send_flags = 0;
	reg_wr.mr = mr;
	reg_wr.key = mr->rkey;
	reg_wr.access = writing ?
	IB_ACCESS_REMOTE_WRITE \| IB_ACCESS_LOCAL_WRITE :
	IB_ACCESS_REMOTE_READ;

	DECR_CQCOUNT(&r_xprt->rx_ep);
	rc = ib_post_send(ia->ri_id->qp, &reg_wr.wr, &bad_wr);
	if (rc)
	goto out_senderr;

	seg1->mr_dir = direction;
	seg1->rl_mw = mw;
	seg1->mr_rkey = mr->rkey;
	seg1->mr_base = mr->iova;
	seg1->mr_nsegs = frmr->sg_nents;
	seg1->mr_len = mr->length;

	return frmr->sg_nents;

	out_senderr:
	dprintk("RPC: %s: ib_post_send status %i\n", __func__, rc);
	ib_dma_unmap_sg(device, frmr->sg, dma_nents, direction);
	__frwr_queue_recovery(mw);
	return rc;
	}

	/* Post a LOCAL_INV Work Request to prevent further remote access
	* via RDMA READ or RDMA WRITE.
	*/
	static int
	frwr_op_unmap(struct rpcrdma_xprt r_xprt, struct rpcrdma_mr_seg seg)
	{
	struct rpcrdma_mr_seg *seg1 = seg;
	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
	struct rpcrdma_mw *mw = seg1->rl_mw;
	struct rpcrdma_frmr *frmr = &mw->r.frmr;
	struct ib_send_wr invalidate_wr, *bad_wr;
	int rc, nsegs = seg->mr_nsegs;

	dprintk("RPC: %s: FRMR %p\n", __func__, mw);

	seg1->rl_mw = NULL;
	frmr->fr_state = FRMR_IS_INVALID;

	memset(&invalidate_wr, 0, sizeof(invalidate_wr));
	invalidate_wr.wr_id = (unsigned long)(void *)mw;
	invalidate_wr.opcode = IB_WR_LOCAL_INV;
	invalidate_wr.ex.invalidate_rkey = frmr->fr_mr->rkey;
	DECR_CQCOUNT(&r_xprt->rx_ep);

	ib_dma_unmap_sg(ia->ri_device, frmr->sg, frmr->sg_nents, seg1->mr_dir);
	read_lock(&ia->ri_qplock);
	rc = ib_post_send(ia->ri_id->qp, &invalidate_wr, &bad_wr);
	read_unlock(&ia->ri_qplock);
	if (rc)
	goto out_err;

	rpcrdma_put_mw(r_xprt, mw);
	return nsegs;

	out_err:
	dprintk("RPC: %s: ib_post_send status %i\n", __func__, rc);
	__frwr_queue_recovery(mw);
	return nsegs;
	}

	static void
	frwr_op_destroy(struct rpcrdma_buffer *buf)
	{
	struct rpcrdma_mw *r;

	/* Ensure stale MWs for "buf" are no longer in flight */
	flush_workqueue(frwr_recovery_wq);

	while (!list_empty(&buf->rb_all)) {
	r = list_entry(buf->rb_all.next, struct rpcrdma_mw, mw_all);
	list_del(&r->mw_all);
	__frwr_release(r);
	kfree(r);
	}
	}

	const struct rpcrdma_memreg_ops rpcrdma_frwr_memreg_ops = {
	.ro_map = frwr_op_map,
	.ro_unmap = frwr_op_unmap,
	.ro_open = frwr_op_open,
	.ro_maxpages = frwr_op_maxpages,
	.ro_init = frwr_op_init,
	.ro_destroy = frwr_op_destroy,
	.ro_displayname = "frwr",
	};