Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1783 insertions, 0 deletions

diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
new file mode 100644
index 000000000..d700bf06b
--- /dev/null
+++ b/drivers/block/drbd/drbd_req.c
@@ -0,0 +1,1783 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+   drbd_req.c
+
+   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+
+   Copyright (C) 2001-2008, LINBIT Information Technologies GmbH.
+   Copyright (C) 1999-2008, Philipp Reisner <philipp.reisner@linbit.com>.
+   Copyright (C) 2002-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
+
+
+ */
+
+#include <linux/module.h>
+
+#include <linux/slab.h>
+#include <linux/drbd.h>
+#include "drbd_int.h"
+#include "drbd_req.h"
+
+
+static bool drbd_may_do_local_read(struct drbd_device *device, sector_t sector, int size);
+
+static struct drbd_request *drbd_req_new(struct drbd_device *device, struct bio *bio_src)
+{
+	struct drbd_request *req;
+
+	req = mempool_alloc(&drbd_request_mempool, GFP_NOIO);
+	if (!req)
+		return NULL;
+	memset(req, 0, sizeof(*req));
+
+	req->rq_state = (bio_data_dir(bio_src) == WRITE ? RQ_WRITE : 0)
+		      | (bio_op(bio_src) == REQ_OP_WRITE_ZEROES ? RQ_ZEROES : 0)
+		      | (bio_op(bio_src) == REQ_OP_DISCARD ? RQ_UNMAP : 0);
+	req->device = device;
+	req->master_bio = bio_src;
+	req->epoch = 0;
+
+	drbd_clear_interval(&req->i);
+	req->i.sector     = bio_src->bi_iter.bi_sector;
+	req->i.size      = bio_src->bi_iter.bi_size;
+	req->i.local = true;
+	req->i.waiting = false;
+
+	INIT_LIST_HEAD(&req->tl_requests);
+	INIT_LIST_HEAD(&req->w.list);
+	INIT_LIST_HEAD(&req->req_pending_master_completion);
+	INIT_LIST_HEAD(&req->req_pending_local);
+
+	/* one reference to be put by __drbd_make_request */
+	atomic_set(&req->completion_ref, 1);
+	/* one kref as long as completion_ref > 0 */
+	kref_init(&req->kref);
+	return req;
+}
+
+static void drbd_remove_request_interval(struct rb_root *root,
+					 struct drbd_request *req)
+{
+	struct drbd_device *device = req->device;
+	struct drbd_interval *i = &req->i;
+
+	drbd_remove_interval(root, i);
+
+	/* Wake up any processes waiting for this request to complete.  */
+	if (i->waiting)
+		wake_up(&device->misc_wait);
+}
+
+void drbd_req_destroy(struct kref *kref)
+{
+	struct drbd_request *req = container_of(kref, struct drbd_request, kref);
+	struct drbd_device *device = req->device;
+	const unsigned s = req->rq_state;
+
+	if ((req->master_bio && !(s & RQ_POSTPONED)) ||
+		atomic_read(&req->completion_ref) ||
+		(s & RQ_LOCAL_PENDING) ||
+		((s & RQ_NET_MASK) && !(s & RQ_NET_DONE))) {
+		drbd_err(device, "drbd_req_destroy: Logic BUG rq_state = 0x%x, completion_ref = %d\n",
+				s, atomic_read(&req->completion_ref));
+		return;
+	}
+
+	/* If called from mod_rq_state (expected normal case) or
+	 * drbd_send_and_submit (the less likely normal path), this holds the
+	 * req_lock, and req->tl_requests will typicaly be on ->transfer_log,
+	 * though it may be still empty (never added to the transfer log).
+	 *
+	 * If called from do_retry(), we do NOT hold the req_lock, but we are
+	 * still allowed to unconditionally list_del(&req->tl_requests),
+	 * because it will be on a local on-stack list only. */
+	list_del_init(&req->tl_requests);
+
+	/* finally remove the request from the conflict detection
+	 * respective block_id verification interval tree. */
+	if (!drbd_interval_empty(&req->i)) {
+		struct rb_root *root;
+
+		if (s & RQ_WRITE)
+			root = &device->write_requests;
+		else
+			root = &device->read_requests;
+		drbd_remove_request_interval(root, req);
+	} else if (s & (RQ_NET_MASK & ~RQ_NET_DONE) && req->i.size != 0)
+		drbd_err(device, "drbd_req_destroy: Logic BUG: interval empty, but: rq_state=0x%x, sect=%llu, size=%u\n",
+			s, (unsigned long long)req->i.sector, req->i.size);
+
+	/* if it was a write, we may have to set the corresponding
+	 * bit(s) out-of-sync first. If it had a local part, we need to
+	 * release the reference to the activity log. */
+	if (s & RQ_WRITE) {
+		/* Set out-of-sync unless both OK flags are set
+		 * (local only or remote failed).
+		 * Other places where we set out-of-sync:
+		 * READ with local io-error */
+
+		/* There is a special case:
+		 * we may notice late that IO was suspended,
+		 * and postpone, or schedule for retry, a write,
+		 * before it even was submitted or sent.
+		 * In that case we do not want to touch the bitmap at all.
+		 */
+		if ((s & (RQ_POSTPONED|RQ_LOCAL_MASK|RQ_NET_MASK)) != RQ_POSTPONED) {
+			if (!(s & RQ_NET_OK) || !(s & RQ_LOCAL_OK))
+				drbd_set_out_of_sync(device, req->i.sector, req->i.size);
+
+			if ((s & RQ_NET_OK) && (s & RQ_LOCAL_OK) && (s & RQ_NET_SIS))
+				drbd_set_in_sync(device, req->i.sector, req->i.size);
+		}
+
+		/* one might be tempted to move the drbd_al_complete_io
+		 * to the local io completion callback drbd_request_endio.
+		 * but, if this was a mirror write, we may only
+		 * drbd_al_complete_io after this is RQ_NET_DONE,
+		 * otherwise the extent could be dropped from the al
+		 * before it has actually been written on the peer.
+		 * if we crash before our peer knows about the request,
+		 * but after the extent has been dropped from the al,
+		 * we would forget to resync the corresponding extent.
+		 */
+		if (s & RQ_IN_ACT_LOG) {
+			if (get_ldev_if_state(device, D_FAILED)) {
+				drbd_al_complete_io(device, &req->i);
+				put_ldev(device);
+			} else if (__ratelimit(&drbd_ratelimit_state)) {
+				drbd_warn(device, "Should have called drbd_al_complete_io(, %llu, %u), "
+					 "but my Disk seems to have failed :(\n",
+					 (unsigned long long) req->i.sector, req->i.size);
+			}
+		}
+	}
+
+	mempool_free(req, &drbd_request_mempool);
+}
+
+static void wake_all_senders(struct drbd_connection *connection)
+{
+	wake_up(&connection->sender_work.q_wait);
+}
+
+/* must hold resource->req_lock */
+void start_new_tl_epoch(struct drbd_connection *connection)
+{
+	/* no point closing an epoch, if it is empty, anyways. */
+	if (connection->current_tle_writes == 0)
+		return;
+
+	connection->current_tle_writes = 0;
+	atomic_inc(&connection->current_tle_nr);
+	wake_all_senders(connection);
+}
+
+void complete_master_bio(struct drbd_device *device,
+		struct bio_and_error *m)
+{
+	if (unlikely(m->error))
+		m->bio->bi_status = errno_to_blk_status(m->error);
+	bio_endio(m->bio);
+	dec_ap_bio(device);
+}
+
+
+/* Helper for __req_mod().
+ * Set m->bio to the master bio, if it is fit to be completed,
+ * or leave it alone (it is initialized to NULL in __req_mod),
+ * if it has already been completed, or cannot be completed yet.
+ * If m->bio is set, the error status to be returned is placed in m->error.
+ */
+static
+void drbd_req_complete(struct drbd_request *req, struct bio_and_error *m)
+{
+	const unsigned s = req->rq_state;
+	struct drbd_device *device = req->device;
+	int error, ok;
+
+	/* we must not complete the master bio, while it is
+	 *	still being processed by _drbd_send_zc_bio (drbd_send_dblock)
+	 *	not yet acknowledged by the peer
+	 *	not yet completed by the local io subsystem
+	 * these flags may get cleared in any order by
+	 *	the worker,
+	 *	the receiver,
+	 *	the bio_endio completion callbacks.
+	 */
+	if ((s & RQ_LOCAL_PENDING && !(s & RQ_LOCAL_ABORTED)) ||
+	    (s & RQ_NET_QUEUED) || (s & RQ_NET_PENDING) ||
+	    (s & RQ_COMPLETION_SUSP)) {
+		drbd_err(device, "drbd_req_complete: Logic BUG rq_state = 0x%x\n", s);
+		return;
+	}
+
+	if (!req->master_bio) {
+		drbd_err(device, "drbd_req_complete: Logic BUG, master_bio == NULL!\n");
+		return;
+	}
+
+	/*
+	 * figure out whether to report success or failure.
+	 *
+	 * report success when at least one of the operations succeeded.
+	 * or, to put the other way,
+	 * only report failure, when both operations failed.
+	 *
+	 * what to do about the failures is handled elsewhere.
+	 * what we need to do here is just: complete the master_bio.
+	 *
+	 * local completion error, if any, has been stored as ERR_PTR
+	 * in private_bio within drbd_request_endio.
+	 */
+	ok = (s & RQ_LOCAL_OK) || (s & RQ_NET_OK);
+	error = PTR_ERR(req->private_bio);
+
+	/* Before we can signal completion to the upper layers,
+	 * we may need to close the current transfer log epoch.
+	 * We are within the request lock, so we can simply compare
+	 * the request epoch number with the current transfer log
+	 * epoch number.  If they match, increase the current_tle_nr,
+	 * and reset the transfer log epoch write_cnt.
+	 */
+	if (op_is_write(bio_op(req->master_bio)) &&
+	    req->epoch == atomic_read(&first_peer_device(device)->connection->current_tle_nr))
+		start_new_tl_epoch(first_peer_device(device)->connection);
+
+	/* Update disk stats */
+	bio_end_io_acct(req->master_bio, req->start_jif);
+
+	/* If READ failed,
+	 * have it be pushed back to the retry work queue,
+	 * so it will re-enter __drbd_make_request(),
+	 * and be re-assigned to a suitable local or remote path,
+	 * or failed if we do not have access to good data anymore.
+	 *
+	 * Unless it was failed early by __drbd_make_request(),
+	 * because no path was available, in which case
+	 * it was not even added to the transfer_log.
+	 *
+	 * read-ahead may fail, and will not be retried.
+	 *
+	 * WRITE should have used all available paths already.
+	 */
+	if (!ok &&
+	    bio_op(req->master_bio) == REQ_OP_READ &&
+	    !(req->master_bio->bi_opf & REQ_RAHEAD) &&
+	    !list_empty(&req->tl_requests))
+		req->rq_state |= RQ_POSTPONED;
+
+	if (!(req->rq_state & RQ_POSTPONED)) {
+		m->error = ok ? 0 : (error ?: -EIO);
+		m->bio = req->master_bio;
+		req->master_bio = NULL;
+		/* We leave it in the tree, to be able to verify later
+		 * write-acks in protocol != C during resync.
+		 * But we mark it as "complete", so it won't be counted as
+		 * conflict in a multi-primary setup. */
+		req->i.completed = true;
+	}
+
+	if (req->i.waiting)
+		wake_up(&device->misc_wait);
+
+	/* Either we are about to complete to upper layers,
+	 * or we will restart this request.
+	 * In either case, the request object will be destroyed soon,
+	 * so better remove it from all lists. */
+	list_del_init(&req->req_pending_master_completion);
+}
+
+/* still holds resource->req_lock */
+static void drbd_req_put_completion_ref(struct drbd_request *req, struct bio_and_error *m, int put)
+{
+	struct drbd_device *device = req->device;
+	D_ASSERT(device, m || (req->rq_state & RQ_POSTPONED));
+
+	if (!put)
+		return;
+
+	if (!atomic_sub_and_test(put, &req->completion_ref))
+		return;
+
+	drbd_req_complete(req, m);
+
+	/* local completion may still come in later,
+	 * we need to keep the req object around. */
+	if (req->rq_state & RQ_LOCAL_ABORTED)
+		return;
+
+	if (req->rq_state & RQ_POSTPONED) {
+		/* don't destroy the req object just yet,
+		 * but queue it for retry */
+		drbd_restart_request(req);
+		return;
+	}
+
+	kref_put(&req->kref, drbd_req_destroy);
+}
+
+static void set_if_null_req_next(struct drbd_peer_device *peer_device, struct drbd_request *req)
+{
+	struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
+	if (!connection)
+		return;
+	if (connection->req_next == NULL)
+		connection->req_next = req;
+}
+
+static void advance_conn_req_next(struct drbd_peer_device *peer_device, struct drbd_request *req)
+{
+	struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
+	struct drbd_request *iter = req;
+	if (!connection)
+		return;
+	if (connection->req_next != req)
+		return;
+
+	req = NULL;
+	list_for_each_entry_continue(iter, &connection->transfer_log, tl_requests) {
+		const unsigned int s = iter->rq_state;
+
+		if (s & RQ_NET_QUEUED) {
+			req = iter;
+			break;
+		}
+	}
+	connection->req_next = req;
+}
+
+static void set_if_null_req_ack_pending(struct drbd_peer_device *peer_device, struct drbd_request *req)
+{
+	struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
+	if (!connection)
+		return;
+	if (connection->req_ack_pending == NULL)
+		connection->req_ack_pending = req;
+}
+
+static void advance_conn_req_ack_pending(struct drbd_peer_device *peer_device, struct drbd_request *req)
+{
+	struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
+	struct drbd_request *iter = req;
+	if (!connection)
+		return;
+	if (connection->req_ack_pending != req)
+		return;
+
+	req = NULL;
+	list_for_each_entry_continue(iter, &connection->transfer_log, tl_requests) {
+		const unsigned int s = iter->rq_state;
+
+		if ((s & RQ_NET_SENT) && (s & RQ_NET_PENDING)) {
+			req = iter;
+			break;
+		}
+	}
+	connection->req_ack_pending = req;
+}
+
+static void set_if_null_req_not_net_done(struct drbd_peer_device *peer_device, struct drbd_request *req)
+{
+	struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
+	if (!connection)
+		return;
+	if (connection->req_not_net_done == NULL)
+		connection->req_not_net_done = req;
+}
+
+static void advance_conn_req_not_net_done(struct drbd_peer_device *peer_device, struct drbd_request *req)
+{
+	struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
+	struct drbd_request *iter = req;
+	if (!connection)
+		return;
+	if (connection->req_not_net_done != req)
+		return;
+
+	req = NULL;
+	list_for_each_entry_continue(iter, &connection->transfer_log, tl_requests) {
+		const unsigned int s = iter->rq_state;
+
+		if ((s & RQ_NET_SENT) && !(s & RQ_NET_DONE)) {
+			req = iter;
+			break;
+		}
+	}
+	connection->req_not_net_done = req;
+}
+
+/* I'd like this to be the only place that manipulates
+ * req->completion_ref and req->kref. */
+static void mod_rq_state(struct drbd_request *req, struct bio_and_error *m,
+		int clear, int set)
+{
+	struct drbd_device *device = req->device;
+	struct drbd_peer_device *peer_device = first_peer_device(device);
+	unsigned s = req->rq_state;
+	int c_put = 0;
+
+	if (drbd_suspended(device) && !((s | clear) & RQ_COMPLETION_SUSP))
+		set |= RQ_COMPLETION_SUSP;
+
+	/* apply */
+
+	req->rq_state &= ~clear;
+	req->rq_state |= set;
+
+	/* no change? */
+	if (req->rq_state == s)
+		return;
+
+	/* intent: get references */
+
+	kref_get(&req->kref);
+
+	if (!(s & RQ_LOCAL_PENDING) && (set & RQ_LOCAL_PENDING))
+		atomic_inc(&req->completion_ref);
+
+	if (!(s & RQ_NET_PENDING) && (set & RQ_NET_PENDING)) {
+		inc_ap_pending(device);
+		atomic_inc(&req->completion_ref);
+	}
+
+	if (!(s & RQ_NET_QUEUED) && (set & RQ_NET_QUEUED)) {
+		atomic_inc(&req->completion_ref);
+		set_if_null_req_next(peer_device, req);
+	}
+
+	if (!(s & RQ_EXP_BARR_ACK) && (set & RQ_EXP_BARR_ACK))
+		kref_get(&req->kref); /* wait for the DONE */
+
+	if (!(s & RQ_NET_SENT) && (set & RQ_NET_SENT)) {
+		/* potentially already completed in the ack_receiver thread */
+		if (!(s & RQ_NET_DONE)) {
+			atomic_add(req->i.size >> 9, &device->ap_in_flight);
+			set_if_null_req_not_net_done(peer_device, req);
+		}
+		if (req->rq_state & RQ_NET_PENDING)
+			set_if_null_req_ack_pending(peer_device, req);
+	}
+
+	if (!(s & RQ_COMPLETION_SUSP) && (set & RQ_COMPLETION_SUSP))
+		atomic_inc(&req->completion_ref);
+
+	/* progress: put references */
+
+	if ((s & RQ_COMPLETION_SUSP) && (clear & RQ_COMPLETION_SUSP))
+		++c_put;
+
+	if (!(s & RQ_LOCAL_ABORTED) && (set & RQ_LOCAL_ABORTED)) {
+		D_ASSERT(device, req->rq_state & RQ_LOCAL_PENDING);
+		++c_put;
+	}
+
+	if ((s & RQ_LOCAL_PENDING) && (clear & RQ_LOCAL_PENDING)) {
+		if (req->rq_state & RQ_LOCAL_ABORTED)
+			kref_put(&req->kref, drbd_req_destroy);
+		else
+			++c_put;
+		list_del_init(&req->req_pending_local);
+	}
+
+	if ((s & RQ_NET_PENDING) && (clear & RQ_NET_PENDING)) {
+		dec_ap_pending(device);
+		++c_put;
+		req->acked_jif = jiffies;
+		advance_conn_req_ack_pending(peer_device, req);
+	}
+
+	if ((s & RQ_NET_QUEUED) && (clear & RQ_NET_QUEUED)) {
+		++c_put;
+		advance_conn_req_next(peer_device, req);
+	}
+
+	if (!(s & RQ_NET_DONE) && (set & RQ_NET_DONE)) {
+		if (s & RQ_NET_SENT)
+			atomic_sub(req->i.size >> 9, &device->ap_in_flight);
+		if (s & RQ_EXP_BARR_ACK)
+			kref_put(&req->kref, drbd_req_destroy);
+		req->net_done_jif = jiffies;
+
+		/* in ahead/behind mode, or just in case,
+		 * before we finally destroy this request,
+		 * the caching pointers must not reference it anymore */
+		advance_conn_req_next(peer_device, req);
+		advance_conn_req_ack_pending(peer_device, req);
+		advance_conn_req_not_net_done(peer_device, req);
+	}
+
+	/* potentially complete and destroy */
+
+	/* If we made progress, retry conflicting peer requests, if any. */
+	if (req->i.waiting)
+		wake_up(&device->misc_wait);
+
+	drbd_req_put_completion_ref(req, m, c_put);
+	kref_put(&req->kref, drbd_req_destroy);
+}
+
+static void drbd_report_io_error(struct drbd_device *device, struct drbd_request *req)
+{
+	if (!__ratelimit(&drbd_ratelimit_state))
+		return;
+
+	drbd_warn(device, "local %s IO error sector %llu+%u on %pg\n",
+			(req->rq_state & RQ_WRITE) ? "WRITE" : "READ",
+			(unsigned long long)req->i.sector,
+			req->i.size >> 9,
+			device->ldev->backing_bdev);
+}
+
+/* Helper for HANDED_OVER_TO_NETWORK.
+ * Is this a protocol A write (neither WRITE_ACK nor RECEIVE_ACK expected)?
+ * Is it also still "PENDING"?
+ * --> If so, clear PENDING and set NET_OK below.
+ * If it is a protocol A write, but not RQ_PENDING anymore, neg-ack was faster
+ * (and we must not set RQ_NET_OK) */
+static inline bool is_pending_write_protocol_A(struct drbd_request *req)
+{
+	return (req->rq_state &
+		   (RQ_WRITE|RQ_NET_PENDING|RQ_EXP_WRITE_ACK|RQ_EXP_RECEIVE_ACK))
+		== (RQ_WRITE|RQ_NET_PENDING);
+}
+
+/* obviously this could be coded as many single functions
+ * instead of one huge switch,
+ * or by putting the code directly in the respective locations
+ * (as it has been before).
+ *
+ * but having it this way
+ *  enforces that it is all in this one place, where it is easier to audit,
+ *  it makes it obvious that whatever "event" "happens" to a request should
+ *  happen "atomically" within the req_lock,
+ *  and it enforces that we have to think in a very structured manner
+ *  about the "events" that may happen to a request during its life time ...
+ */
+int __req_mod(struct drbd_request *req, enum drbd_req_event what,
+		struct bio_and_error *m)
+{
+	struct drbd_device *const device = req->device;
+	struct drbd_peer_device *const peer_device = first_peer_device(device);
+	struct drbd_connection *const connection = peer_device ? peer_device->connection : NULL;
+	struct net_conf *nc;
+	int p, rv = 0;
+
+	if (m)
+		m->bio = NULL;
+
+	switch (what) {
+	default:
+		drbd_err(device, "LOGIC BUG in %s:%u\n", __FILE__ , __LINE__);
+		break;
+
+	/* does not happen...
+	 * initialization done in drbd_req_new
+	case CREATED:
+		break;
+		*/
+
+	case TO_BE_SENT: /* via network */
+		/* reached via __drbd_make_request
+		 * and from w_read_retry_remote */
+		D_ASSERT(device, !(req->rq_state & RQ_NET_MASK));
+		rcu_read_lock();
+		nc = rcu_dereference(connection->net_conf);
+		p = nc->wire_protocol;
+		rcu_read_unlock();
+		req->rq_state |=
+			p == DRBD_PROT_C ? RQ_EXP_WRITE_ACK :
+			p == DRBD_PROT_B ? RQ_EXP_RECEIVE_ACK : 0;
+		mod_rq_state(req, m, 0, RQ_NET_PENDING);
+		break;
+
+	case TO_BE_SUBMITTED: /* locally */
+		/* reached via __drbd_make_request */
+		D_ASSERT(device, !(req->rq_state & RQ_LOCAL_MASK));
+		mod_rq_state(req, m, 0, RQ_LOCAL_PENDING);
+		break;
+
+	case COMPLETED_OK:
+		if (req->rq_state & RQ_WRITE)
+			device->writ_cnt += req->i.size >> 9;
+		else
+			device->read_cnt += req->i.size >> 9;
+
+		mod_rq_state(req, m, RQ_LOCAL_PENDING,
+				RQ_LOCAL_COMPLETED|RQ_LOCAL_OK);
+		break;
+
+	case ABORT_DISK_IO:
+		mod_rq_state(req, m, 0, RQ_LOCAL_ABORTED);
+		break;
+
+	case WRITE_COMPLETED_WITH_ERROR:
+		drbd_report_io_error(device, req);
+		__drbd_chk_io_error(device, DRBD_WRITE_ERROR);
+		mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
+		break;
+
+	case READ_COMPLETED_WITH_ERROR:
+		drbd_set_out_of_sync(device, req->i.sector, req->i.size);
+		drbd_report_io_error(device, req);
+		__drbd_chk_io_error(device, DRBD_READ_ERROR);
+		fallthrough;
+	case READ_AHEAD_COMPLETED_WITH_ERROR:
+		/* it is legal to fail read-ahead, no __drbd_chk_io_error in that case. */
+		mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
+		break;
+
+	case DISCARD_COMPLETED_NOTSUPP:
+	case DISCARD_COMPLETED_WITH_ERROR:
+		/* I'd rather not detach from local disk just because it
+		 * failed a REQ_OP_DISCARD. */
+		mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
+		break;
+
+	case QUEUE_FOR_NET_READ:
+		/* READ, and
+		 * no local disk,
+		 * or target area marked as invalid,
+		 * or just got an io-error. */
+		/* from __drbd_make_request
+		 * or from bio_endio during read io-error recovery */
+
+		/* So we can verify the handle in the answer packet.
+		 * Corresponding drbd_remove_request_interval is in
+		 * drbd_req_complete() */
+		D_ASSERT(device, drbd_interval_empty(&req->i));
+		drbd_insert_interval(&device->read_requests, &req->i);
+
+		set_bit(UNPLUG_REMOTE, &device->flags);
+
+		D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
+		D_ASSERT(device, (req->rq_state & RQ_LOCAL_MASK) == 0);
+		mod_rq_state(req, m, 0, RQ_NET_QUEUED);
+		req->w.cb = w_send_read_req;
+		drbd_queue_work(&connection->sender_work,
+				&req->w);
+		break;
+
+	case QUEUE_FOR_NET_WRITE:
+		/* assert something? */
+		/* from __drbd_make_request only */
+
+		/* Corresponding drbd_remove_request_interval is in
+		 * drbd_req_complete() */
+		D_ASSERT(device, drbd_interval_empty(&req->i));
+		drbd_insert_interval(&device->write_requests, &req->i);
+
+		/* NOTE
+		 * In case the req ended up on the transfer log before being
+		 * queued on the worker, it could lead to this request being
+		 * missed during cleanup after connection loss.
+		 * So we have to do both operations here,
+		 * within the same lock that protects the transfer log.
+		 *
+		 * _req_add_to_epoch(req); this has to be after the
+		 * _maybe_start_new_epoch(req); which happened in
+		 * __drbd_make_request, because we now may set the bit
+		 * again ourselves to close the current epoch.
+		 *
+		 * Add req to the (now) current epoch (barrier). */
+
+		/* otherwise we may lose an unplug, which may cause some remote
+		 * io-scheduler timeout to expire, increasing maximum latency,
+		 * hurting performance. */
+		set_bit(UNPLUG_REMOTE, &device->flags);
+
+		/* queue work item to send data */
+		D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
+		mod_rq_state(req, m, 0, RQ_NET_QUEUED|RQ_EXP_BARR_ACK);
+		req->w.cb =  w_send_dblock;
+		drbd_queue_work(&connection->sender_work,
+				&req->w);
+
+		/* close the epoch, in case it outgrew the limit */
+		rcu_read_lock();
+		nc = rcu_dereference(connection->net_conf);
+		p = nc->max_epoch_size;
+		rcu_read_unlock();
+		if (connection->current_tle_writes >= p)
+			start_new_tl_epoch(connection);
+
+		break;
+
+	case QUEUE_FOR_SEND_OOS:
+		mod_rq_state(req, m, 0, RQ_NET_QUEUED);
+		req->w.cb =  w_send_out_of_sync;
+		drbd_queue_work(&connection->sender_work,
+				&req->w);
+		break;
+
+	case READ_RETRY_REMOTE_CANCELED:
+	case SEND_CANCELED:
+	case SEND_FAILED:
+		/* real cleanup will be done from tl_clear.  just update flags
+		 * so it is no longer marked as on the worker queue */
+		mod_rq_state(req, m, RQ_NET_QUEUED, 0);
+		break;
+
+	case HANDED_OVER_TO_NETWORK:
+		/* assert something? */
+		if (is_pending_write_protocol_A(req))
+			/* this is what is dangerous about protocol A:
+			 * pretend it was successfully written on the peer. */
+			mod_rq_state(req, m, RQ_NET_QUEUED|RQ_NET_PENDING,
+						RQ_NET_SENT|RQ_NET_OK);
+		else
+			mod_rq_state(req, m, RQ_NET_QUEUED, RQ_NET_SENT);
+		/* It is still not yet RQ_NET_DONE until the
+		 * corresponding epoch barrier got acked as well,
+		 * so we know what to dirty on connection loss. */
+		break;
+
+	case OOS_HANDED_TO_NETWORK:
+		/* Was not set PENDING, no longer QUEUED, so is now DONE
+		 * as far as this connection is concerned. */
+		mod_rq_state(req, m, RQ_NET_QUEUED, RQ_NET_DONE);
+		break;
+
+	case CONNECTION_LOST_WHILE_PENDING:
+		/* transfer log cleanup after connection loss */
+		mod_rq_state(req, m,
+				RQ_NET_OK|RQ_NET_PENDING|RQ_COMPLETION_SUSP,
+				RQ_NET_DONE);
+		break;
+
+	case CONFLICT_RESOLVED:
+		/* for superseded conflicting writes of multiple primaries,
+		 * there is no need to keep anything in the tl, potential
+		 * node crashes are covered by the activity log.
+		 *
+		 * If this request had been marked as RQ_POSTPONED before,
+		 * it will actually not be completed, but "restarted",
+		 * resubmitted from the retry worker context. */
+		D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
+		D_ASSERT(device, req->rq_state & RQ_EXP_WRITE_ACK);
+		mod_rq_state(req, m, RQ_NET_PENDING, RQ_NET_DONE|RQ_NET_OK);
+		break;
+
+	case WRITE_ACKED_BY_PEER_AND_SIS:
+		req->rq_state |= RQ_NET_SIS;
+		fallthrough;
+	case WRITE_ACKED_BY_PEER:
+		/* Normal operation protocol C: successfully written on peer.
+		 * During resync, even in protocol != C,
+		 * we requested an explicit write ack anyways.
+		 * Which means we cannot even assert anything here.
+		 * Nothing more to do here.
+		 * We want to keep the tl in place for all protocols, to cater
+		 * for volatile write-back caches on lower level devices. */
+		goto ack_common;
+	case RECV_ACKED_BY_PEER:
+		D_ASSERT(device, req->rq_state & RQ_EXP_RECEIVE_ACK);
+		/* protocol B; pretends to be successfully written on peer.
+		 * see also notes above in HANDED_OVER_TO_NETWORK about
+		 * protocol != C */
+	ack_common:
+		mod_rq_state(req, m, RQ_NET_PENDING, RQ_NET_OK);
+		break;
+
+	case POSTPONE_WRITE:
+		D_ASSERT(device, req->rq_state & RQ_EXP_WRITE_ACK);
+		/* If this node has already detected the write conflict, the
+		 * worker will be waiting on misc_wait.  Wake it up once this
+		 * request has completed locally.
+		 */
+		D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
+		req->rq_state |= RQ_POSTPONED;
+		if (req->i.waiting)
+			wake_up(&device->misc_wait);
+		/* Do not clear RQ_NET_PENDING. This request will make further
+		 * progress via restart_conflicting_writes() or
+		 * fail_postponed_requests(). Hopefully. */
+		break;
+
+	case NEG_ACKED:
+		mod_rq_state(req, m, RQ_NET_OK|RQ_NET_PENDING, 0);
+		break;
+
+	case FAIL_FROZEN_DISK_IO:
+		if (!(req->rq_state & RQ_LOCAL_COMPLETED))
+			break;
+		mod_rq_state(req, m, RQ_COMPLETION_SUSP, 0);
+		break;
+
+	case RESTART_FROZEN_DISK_IO:
+		if (!(req->rq_state & RQ_LOCAL_COMPLETED))
+			break;
+
+		mod_rq_state(req, m,
+				RQ_COMPLETION_SUSP|RQ_LOCAL_COMPLETED,
+				RQ_LOCAL_PENDING);
+
+		rv = MR_READ;
+		if (bio_data_dir(req->master_bio) == WRITE)
+			rv = MR_WRITE;
+
+		get_ldev(device); /* always succeeds in this call path */
+		req->w.cb = w_restart_disk_io;
+		drbd_queue_work(&connection->sender_work,
+				&req->w);
+		break;
+
+	case RESEND:
+		/* Simply complete (local only) READs. */
+		if (!(req->rq_state & RQ_WRITE) && !req->w.cb) {
+			mod_rq_state(req, m, RQ_COMPLETION_SUSP, 0);
+			break;
+		}
+
+		/* If RQ_NET_OK is already set, we got a P_WRITE_ACK or P_RECV_ACK
+		   before the connection loss (B&C only); only P_BARRIER_ACK
+		   (or the local completion?) was missing when we suspended.
+		   Throwing them out of the TL here by pretending we got a BARRIER_ACK.
+		   During connection handshake, we ensure that the peer was not rebooted. */
+		if (!(req->rq_state & RQ_NET_OK)) {
+			/* FIXME could this possibly be a req->dw.cb == w_send_out_of_sync?
+			 * in that case we must not set RQ_NET_PENDING. */
+
+			mod_rq_state(req, m, RQ_COMPLETION_SUSP, RQ_NET_QUEUED|RQ_NET_PENDING);
+			if (req->w.cb) {
+				/* w.cb expected to be w_send_dblock, or w_send_read_req */
+				drbd_queue_work(&connection->sender_work,
+						&req->w);
+				rv = req->rq_state & RQ_WRITE ? MR_WRITE : MR_READ;
+			} /* else: FIXME can this happen? */
+			break;
+		}
+		fallthrough;	/* to BARRIER_ACKED */
+
+	case BARRIER_ACKED:
+		/* barrier ack for READ requests does not make sense */
+		if (!(req->rq_state & RQ_WRITE))
+			break;
+
+		if (req->rq_state & RQ_NET_PENDING) {
+			/* barrier came in before all requests were acked.
+			 * this is bad, because if the connection is lost now,
+			 * we won't be able to clean them up... */
+			drbd_err(device, "FIXME (BARRIER_ACKED but pending)\n");
+		}
+		/* Allowed to complete requests, even while suspended.
+		 * As this is called for all requests within a matching epoch,
+		 * we need to filter, and only set RQ_NET_DONE for those that
+		 * have actually been on the wire. */
+		mod_rq_state(req, m, RQ_COMPLETION_SUSP,
+				(req->rq_state & RQ_NET_MASK) ? RQ_NET_DONE : 0);
+		break;
+
+	case DATA_RECEIVED:
+		D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
+		mod_rq_state(req, m, RQ_NET_PENDING, RQ_NET_OK|RQ_NET_DONE);
+		break;
+
+	case QUEUE_AS_DRBD_BARRIER:
+		start_new_tl_epoch(connection);
+		mod_rq_state(req, m, 0, RQ_NET_OK|RQ_NET_DONE);
+		break;
+	}
+
+	return rv;
+}
+
+/* we may do a local read if:
+ * - we are consistent (of course),
+ * - or we are generally inconsistent,
+ *   BUT we are still/already IN SYNC for this area.
+ *   since size may be bigger than BM_BLOCK_SIZE,
+ *   we may need to check several bits.
+ */
+static bool drbd_may_do_local_read(struct drbd_device *device, sector_t sector, int size)
+{
+	unsigned long sbnr, ebnr;
+	sector_t esector, nr_sectors;
+
+	if (device->state.disk == D_UP_TO_DATE)
+		return true;
+	if (device->state.disk != D_INCONSISTENT)
+		return false;
+	esector = sector + (size >> 9) - 1;
+	nr_sectors = get_capacity(device->vdisk);
+	D_ASSERT(device, sector  < nr_sectors);
+	D_ASSERT(device, esector < nr_sectors);
+
+	sbnr = BM_SECT_TO_BIT(sector);
+	ebnr = BM_SECT_TO_BIT(esector);
+
+	return drbd_bm_count_bits(device, sbnr, ebnr) == 0;
+}
+
+static bool remote_due_to_read_balancing(struct drbd_device *device, sector_t sector,
+		enum drbd_read_balancing rbm)
+{
+	int stripe_shift;
+
+	switch (rbm) {
+	case RB_CONGESTED_REMOTE:
+		return false;
+	case RB_LEAST_PENDING:
+		return atomic_read(&device->local_cnt) >
+			atomic_read(&device->ap_pending_cnt) + atomic_read(&device->rs_pending_cnt);
+	case RB_32K_STRIPING:  /* stripe_shift = 15 */
+	case RB_64K_STRIPING:
+	case RB_128K_STRIPING:
+	case RB_256K_STRIPING:
+	case RB_512K_STRIPING:
+	case RB_1M_STRIPING:   /* stripe_shift = 20 */
+		stripe_shift = (rbm - RB_32K_STRIPING + 15);
+		return (sector >> (stripe_shift - 9)) & 1;
+	case RB_ROUND_ROBIN:
+		return test_and_change_bit(READ_BALANCE_RR, &device->flags);
+	case RB_PREFER_REMOTE:
+		return true;
+	case RB_PREFER_LOCAL:
+	default:
+		return false;
+	}
+}
+
+/*
+ * complete_conflicting_writes  -  wait for any conflicting write requests
+ *
+ * The write_requests tree contains all active write requests which we
+ * currently know about.  Wait for any requests to complete which conflict with
+ * the new one.
+ *
+ * Only way out: remove the conflicting intervals from the tree.
+ */
+static void complete_conflicting_writes(struct drbd_request *req)
+{
+	DEFINE_WAIT(wait);
+	struct drbd_device *device = req->device;
+	struct drbd_interval *i;
+	sector_t sector = req->i.sector;
+	int size = req->i.size;
+
+	for (;;) {
+		drbd_for_each_overlap(i, &device->write_requests, sector, size) {
+			/* Ignore, if already completed to upper layers. */
+			if (i->completed)
+				continue;
+			/* Handle the first found overlap.  After the schedule
+			 * we have to restart the tree walk. */
+			break;
+		}
+		if (!i)	/* if any */
+			break;
+
+		/* Indicate to wake up device->misc_wait on progress.  */
+		prepare_to_wait(&device->misc_wait, &wait, TASK_UNINTERRUPTIBLE);
+		i->waiting = true;
+		spin_unlock_irq(&device->resource->req_lock);
+		schedule();
+		spin_lock_irq(&device->resource->req_lock);
+	}
+	finish_wait(&device->misc_wait, &wait);
+}
+
+/* called within req_lock */
+static void maybe_pull_ahead(struct drbd_device *device)
+{
+	struct drbd_connection *connection = first_peer_device(device)->connection;
+	struct net_conf *nc;
+	bool congested = false;
+	enum drbd_on_congestion on_congestion;
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	on_congestion = nc ? nc->on_congestion : OC_BLOCK;
+	rcu_read_unlock();
+	if (on_congestion == OC_BLOCK ||
+	    connection->agreed_pro_version < 96)
+		return;
+
+	if (on_congestion == OC_PULL_AHEAD && device->state.conn == C_AHEAD)
+		return; /* nothing to do ... */
+
+	/* If I don't even have good local storage, we can not reasonably try
+	 * to pull ahead of the peer. We also need the local reference to make
+	 * sure device->act_log is there.
+	 */
+	if (!get_ldev_if_state(device, D_UP_TO_DATE))
+		return;
+
+	if (nc->cong_fill &&
+	    atomic_read(&device->ap_in_flight) >= nc->cong_fill) {
+		drbd_info(device, "Congestion-fill threshold reached\n");
+		congested = true;
+	}
+
+	if (device->act_log->used >= nc->cong_extents) {
+		drbd_info(device, "Congestion-extents threshold reached\n");
+		congested = true;
+	}
+
+	if (congested) {
+		/* start a new epoch for non-mirrored writes */
+		start_new_tl_epoch(first_peer_device(device)->connection);
+
+		if (on_congestion == OC_PULL_AHEAD)
+			_drbd_set_state(_NS(device, conn, C_AHEAD), 0, NULL);
+		else  /*nc->on_congestion == OC_DISCONNECT */
+			_drbd_set_state(_NS(device, conn, C_DISCONNECTING), 0, NULL);
+	}
+	put_ldev(device);
+}
+
+/* If this returns false, and req->private_bio is still set,
+ * this should be submitted locally.
+ *
+ * If it returns false, but req->private_bio is not set,
+ * we do not have access to good data :(
+ *
+ * Otherwise, this destroys req->private_bio, if any,
+ * and returns true.
+ */
+static bool do_remote_read(struct drbd_request *req)
+{
+	struct drbd_device *device = req->device;
+	enum drbd_read_balancing rbm;
+
+	if (req->private_bio) {
+		if (!drbd_may_do_local_read(device,
+					req->i.sector, req->i.size)) {
+			bio_put(req->private_bio);
+			req->private_bio = NULL;
+			put_ldev(device);
+		}
+	}
+
+	if (device->state.pdsk != D_UP_TO_DATE)
+		return false;
+
+	if (req->private_bio == NULL)
+		return true;
+
+	/* TODO: improve read balancing decisions, take into account drbd
+	 * protocol, pending requests etc. */
+
+	rcu_read_lock();
+	rbm = rcu_dereference(device->ldev->disk_conf)->read_balancing;
+	rcu_read_unlock();
+
+	if (rbm == RB_PREFER_LOCAL && req->private_bio)
+		return false; /* submit locally */
+
+	if (remote_due_to_read_balancing(device, req->i.sector, rbm)) {
+		if (req->private_bio) {
+			bio_put(req->private_bio);
+			req->private_bio = NULL;
+			put_ldev(device);
+		}
+		return true;
+	}
+
+	return false;
+}
+
+bool drbd_should_do_remote(union drbd_dev_state s)
+{
+	return s.pdsk == D_UP_TO_DATE ||
+		(s.pdsk >= D_INCONSISTENT &&
+		 s.conn >= C_WF_BITMAP_T &&
+		 s.conn < C_AHEAD);
+	/* Before proto 96 that was >= CONNECTED instead of >= C_WF_BITMAP_T.
+	   That is equivalent since before 96 IO was frozen in the C_WF_BITMAP*
+	   states. */
+}
+
+static bool drbd_should_send_out_of_sync(union drbd_dev_state s)
+{
+	return s.conn == C_AHEAD || s.conn == C_WF_BITMAP_S;
+	/* pdsk = D_INCONSISTENT as a consequence. Protocol 96 check not necessary
+	   since we enter state C_AHEAD only if proto >= 96 */
+}
+
+/* returns number of connections (== 1, for drbd 8.4)
+ * expected to actually write this data,
+ * which does NOT include those that we are L_AHEAD for. */
+static int drbd_process_write_request(struct drbd_request *req)
+{
+	struct drbd_device *device = req->device;
+	int remote, send_oos;
+
+	remote = drbd_should_do_remote(device->state);
+	send_oos = drbd_should_send_out_of_sync(device->state);
+
+	/* Need to replicate writes.  Unless it is an empty flush,
+	 * which is better mapped to a DRBD P_BARRIER packet,
+	 * also for drbd wire protocol compatibility reasons.
+	 * If this was a flush, just start a new epoch.
+	 * Unless the current epoch was empty anyways, or we are not currently
+	 * replicating, in which case there is no point. */
+	if (unlikely(req->i.size == 0)) {
+		/* The only size==0 bios we expect are empty flushes. */
+		D_ASSERT(device, req->master_bio->bi_opf & REQ_PREFLUSH);
+		if (remote)
+			_req_mod(req, QUEUE_AS_DRBD_BARRIER);
+		return remote;
+	}
+
+	if (!remote && !send_oos)
+		return 0;
+
+	D_ASSERT(device, !(remote && send_oos));
+
+	if (remote) {
+		_req_mod(req, TO_BE_SENT);
+		_req_mod(req, QUEUE_FOR_NET_WRITE);
+	} else if (drbd_set_out_of_sync(device, req->i.sector, req->i.size))
+		_req_mod(req, QUEUE_FOR_SEND_OOS);
+
+	return remote;
+}
+
+static void drbd_process_discard_or_zeroes_req(struct drbd_request *req, int flags)
+{
+	int err = drbd_issue_discard_or_zero_out(req->device,
+				req->i.sector, req->i.size >> 9, flags);
+	if (err)
+		req->private_bio->bi_status = BLK_STS_IOERR;
+	bio_endio(req->private_bio);
+}
+
+static void
+drbd_submit_req_private_bio(struct drbd_request *req)
+{
+	struct drbd_device *device = req->device;
+	struct bio *bio = req->private_bio;
+	unsigned int type;
+
+	if (bio_op(bio) != REQ_OP_READ)
+		type = DRBD_FAULT_DT_WR;
+	else if (bio->bi_opf & REQ_RAHEAD)
+		type = DRBD_FAULT_DT_RA;
+	else
+		type = DRBD_FAULT_DT_RD;
+
+	/* State may have changed since we grabbed our reference on the
+	 * ->ldev member. Double check, and short-circuit to endio.
+	 * In case the last activity log transaction failed to get on
+	 * stable storage, and this is a WRITE, we may not even submit
+	 * this bio. */
+	if (get_ldev(device)) {
+		if (drbd_insert_fault(device, type))
+			bio_io_error(bio);
+		else if (bio_op(bio) == REQ_OP_WRITE_ZEROES)
+			drbd_process_discard_or_zeroes_req(req, EE_ZEROOUT |
+			    ((bio->bi_opf & REQ_NOUNMAP) ? 0 : EE_TRIM));
+		else if (bio_op(bio) == REQ_OP_DISCARD)
+			drbd_process_discard_or_zeroes_req(req, EE_TRIM);
+		else
+			submit_bio_noacct(bio);
+		put_ldev(device);
+	} else
+		bio_io_error(bio);
+}
+
+static void drbd_queue_write(struct drbd_device *device, struct drbd_request *req)
+{
+	spin_lock_irq(&device->resource->req_lock);
+	list_add_tail(&req->tl_requests, &device->submit.writes);
+	list_add_tail(&req->req_pending_master_completion,
+			&device->pending_master_completion[1 /* WRITE */]);
+	spin_unlock_irq(&device->resource->req_lock);
+	queue_work(device->submit.wq, &device->submit.worker);
+	/* do_submit() may sleep internally on al_wait, too */
+	wake_up(&device->al_wait);
+}
+
+/* returns the new drbd_request pointer, if the caller is expected to
+ * drbd_send_and_submit() it (to save latency), or NULL if we queued the
+ * request on the submitter thread.
+ * Returns ERR_PTR(-ENOMEM) if we cannot allocate a drbd_request.
+ */
+static struct drbd_request *
+drbd_request_prepare(struct drbd_device *device, struct bio *bio)
+{
+	const int rw = bio_data_dir(bio);
+	struct drbd_request *req;
+
+	/* allocate outside of all locks; */
+	req = drbd_req_new(device, bio);
+	if (!req) {
+		dec_ap_bio(device);
+		/* only pass the error to the upper layers.
+		 * if user cannot handle io errors, that's not our business. */
+		drbd_err(device, "could not kmalloc() req\n");
+		bio->bi_status = BLK_STS_RESOURCE;
+		bio_endio(bio);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	/* Update disk stats */
+	req->start_jif = bio_start_io_acct(req->master_bio);
+
+	if (get_ldev(device)) {
+		req->private_bio = bio_alloc_clone(device->ldev->backing_bdev,
+						   bio, GFP_NOIO,
+						   &drbd_io_bio_set);
+		req->private_bio->bi_private = req;
+		req->private_bio->bi_end_io = drbd_request_endio;
+	}
+
+	/* process discards always from our submitter thread */
+	if (bio_op(bio) == REQ_OP_WRITE_ZEROES ||
+	    bio_op(bio) == REQ_OP_DISCARD)
+		goto queue_for_submitter_thread;
+
+	if (rw == WRITE && req->private_bio && req->i.size
+	&& !test_bit(AL_SUSPENDED, &device->flags)) {
+		if (!drbd_al_begin_io_fastpath(device, &req->i))
+			goto queue_for_submitter_thread;
+		req->rq_state |= RQ_IN_ACT_LOG;
+		req->in_actlog_jif = jiffies;
+	}
+	return req;
+
+ queue_for_submitter_thread:
+	atomic_inc(&device->ap_actlog_cnt);
+	drbd_queue_write(device, req);
+	return NULL;
+}
+
+/* Require at least one path to current data.
+ * We don't want to allow writes on C_STANDALONE D_INCONSISTENT:
+ * We would not allow to read what was written,
+ * we would not have bumped the data generation uuids,
+ * we would cause data divergence for all the wrong reasons.
+ *
+ * If we don't see at least one D_UP_TO_DATE, we will fail this request,
+ * which either returns EIO, or, if OND_SUSPEND_IO is set, suspends IO,
+ * and queues for retry later.
+ */
+static bool may_do_writes(struct drbd_device *device)
+{
+	const union drbd_dev_state s = device->state;
+	return s.disk == D_UP_TO_DATE || s.pdsk == D_UP_TO_DATE;
+}
+
+struct drbd_plug_cb {
+	struct blk_plug_cb cb;
+	struct drbd_request *most_recent_req;
+	/* do we need more? */
+};
+
+static void drbd_unplug(struct blk_plug_cb *cb, bool from_schedule)
+{
+	struct drbd_plug_cb *plug = container_of(cb, struct drbd_plug_cb, cb);
+	struct drbd_resource *resource = plug->cb.data;
+	struct drbd_request *req = plug->most_recent_req;
+
+	kfree(cb);
+	if (!req)
+		return;
+
+	spin_lock_irq(&resource->req_lock);
+	/* In case the sender did not process it yet, raise the flag to
+	 * have it followed with P_UNPLUG_REMOTE just after. */
+	req->rq_state |= RQ_UNPLUG;
+	/* but also queue a generic unplug */
+	drbd_queue_unplug(req->device);
+	kref_put(&req->kref, drbd_req_destroy);
+	spin_unlock_irq(&resource->req_lock);
+}
+
+static struct drbd_plug_cb* drbd_check_plugged(struct drbd_resource *resource)
+{
+	/* A lot of text to say
+	 * return (struct drbd_plug_cb*)blk_check_plugged(); */
+	struct drbd_plug_cb *plug;
+	struct blk_plug_cb *cb = blk_check_plugged(drbd_unplug, resource, sizeof(*plug));
+
+	if (cb)
+		plug = container_of(cb, struct drbd_plug_cb, cb);
+	else
+		plug = NULL;
+	return plug;
+}
+
+static void drbd_update_plug(struct drbd_plug_cb *plug, struct drbd_request *req)
+{
+	struct drbd_request *tmp = plug->most_recent_req;
+	/* Will be sent to some peer.
+	 * Remember to tag it with UNPLUG_REMOTE on unplug */
+	kref_get(&req->kref);
+	plug->most_recent_req = req;
+	if (tmp)
+		kref_put(&tmp->kref, drbd_req_destroy);
+}
+
+static void drbd_send_and_submit(struct drbd_device *device, struct drbd_request *req)
+{
+	struct drbd_resource *resource = device->resource;
+	const int rw = bio_data_dir(req->master_bio);
+	struct bio_and_error m = { NULL, };
+	bool no_remote = false;
+	bool submit_private_bio = false;
+
+	spin_lock_irq(&resource->req_lock);
+	if (rw == WRITE) {
+		/* This may temporarily give up the req_lock,
+		 * but will re-aquire it before it returns here.
+		 * Needs to be before the check on drbd_suspended() */
+		complete_conflicting_writes(req);
+		/* no more giving up req_lock from now on! */
+
+		/* check for congestion, and potentially stop sending
+		 * full data updates, but start sending "dirty bits" only. */
+		maybe_pull_ahead(device);
+	}
+
+
+	if (drbd_suspended(device)) {
+		/* push back and retry: */
+		req->rq_state |= RQ_POSTPONED;
+		if (req->private_bio) {
+			bio_put(req->private_bio);
+			req->private_bio = NULL;
+			put_ldev(device);
+		}
+		goto out;
+	}
+
+	/* We fail READ early, if we can not serve it.
+	 * We must do this before req is registered on any lists.
+	 * Otherwise, drbd_req_complete() will queue failed READ for retry. */
+	if (rw != WRITE) {
+		if (!do_remote_read(req) && !req->private_bio)
+			goto nodata;
+	}
+
+	/* which transfer log epoch does this belong to? */
+	req->epoch = atomic_read(&first_peer_device(device)->connection->current_tle_nr);
+
+	/* no point in adding empty flushes to the transfer log,
+	 * they are mapped to drbd barriers already. */
+	if (likely(req->i.size!=0)) {
+		if (rw == WRITE)
+			first_peer_device(device)->connection->current_tle_writes++;
+
+		list_add_tail(&req->tl_requests, &first_peer_device(device)->connection->transfer_log);
+	}
+
+	if (rw == WRITE) {
+		if (req->private_bio && !may_do_writes(device)) {
+			bio_put(req->private_bio);
+			req->private_bio = NULL;
+			put_ldev(device);
+			goto nodata;
+		}
+		if (!drbd_process_write_request(req))
+			no_remote = true;
+	} else {
+		/* We either have a private_bio, or we can read from remote.
+		 * Otherwise we had done the goto nodata above. */
+		if (req->private_bio == NULL) {
+			_req_mod(req, TO_BE_SENT);
+			_req_mod(req, QUEUE_FOR_NET_READ);
+		} else
+			no_remote = true;
+	}
+
+	if (no_remote == false) {
+		struct drbd_plug_cb *plug = drbd_check_plugged(resource);
+		if (plug)
+			drbd_update_plug(plug, req);
+	}
+
+	/* If it took the fast path in drbd_request_prepare, add it here.
+	 * The slow path has added it already. */
+	if (list_empty(&req->req_pending_master_completion))
+		list_add_tail(&req->req_pending_master_completion,
+			&device->pending_master_completion[rw == WRITE]);
+	if (req->private_bio) {
+		/* needs to be marked within the same spinlock */
+		req->pre_submit_jif = jiffies;
+		list_add_tail(&req->req_pending_local,
+			&device->pending_completion[rw == WRITE]);
+		_req_mod(req, TO_BE_SUBMITTED);
+		/* but we need to give up the spinlock to submit */
+		submit_private_bio = true;
+	} else if (no_remote) {
+nodata:
+		if (__ratelimit(&drbd_ratelimit_state))
+			drbd_err(device, "IO ERROR: neither local nor remote data, sector %llu+%u\n",
+					(unsigned long long)req->i.sector, req->i.size >> 9);
+		/* A write may have been queued for send_oos, however.
+		 * So we can not simply free it, we must go through drbd_req_put_completion_ref() */
+	}
+
+out:
+	drbd_req_put_completion_ref(req, &m, 1);
+	spin_unlock_irq(&resource->req_lock);
+
+	/* Even though above is a kref_put(), this is safe.
+	 * As long as we still need to submit our private bio,
+	 * we hold a completion ref, and the request cannot disappear.
+	 * If however this request did not even have a private bio to submit
+	 * (e.g. remote read), req may already be invalid now.
+	 * That's why we cannot check on req->private_bio. */
+	if (submit_private_bio)
+		drbd_submit_req_private_bio(req);
+	if (m.bio)
+		complete_master_bio(device, &m);
+}
+
+void __drbd_make_request(struct drbd_device *device, struct bio *bio)
+{
+	struct drbd_request *req = drbd_request_prepare(device, bio);
+	if (IS_ERR_OR_NULL(req))
+		return;
+	drbd_send_and_submit(device, req);
+}
+
+static void submit_fast_path(struct drbd_device *device, struct list_head *incoming)
+{
+	struct blk_plug plug;
+	struct drbd_request *req, *tmp;
+
+	blk_start_plug(&plug);
+	list_for_each_entry_safe(req, tmp, incoming, tl_requests) {
+		const int rw = bio_data_dir(req->master_bio);
+
+		if (rw == WRITE /* rw != WRITE should not even end up here! */
+		&& req->private_bio && req->i.size
+		&& !test_bit(AL_SUSPENDED, &device->flags)) {
+			if (!drbd_al_begin_io_fastpath(device, &req->i))
+				continue;
+
+			req->rq_state |= RQ_IN_ACT_LOG;
+			req->in_actlog_jif = jiffies;
+			atomic_dec(&device->ap_actlog_cnt);
+		}
+
+		list_del_init(&req->tl_requests);
+		drbd_send_and_submit(device, req);
+	}
+	blk_finish_plug(&plug);
+}
+
+static bool prepare_al_transaction_nonblock(struct drbd_device *device,
+					    struct list_head *incoming,
+					    struct list_head *pending,
+					    struct list_head *later)
+{
+	struct drbd_request *req;
+	int wake = 0;
+	int err;
+
+	spin_lock_irq(&device->al_lock);
+	while ((req = list_first_entry_or_null(incoming, struct drbd_request, tl_requests))) {
+		err = drbd_al_begin_io_nonblock(device, &req->i);
+		if (err == -ENOBUFS)
+			break;
+		if (err == -EBUSY)
+			wake = 1;
+		if (err)
+			list_move_tail(&req->tl_requests, later);
+		else
+			list_move_tail(&req->tl_requests, pending);
+	}
+	spin_unlock_irq(&device->al_lock);
+	if (wake)
+		wake_up(&device->al_wait);
+	return !list_empty(pending);
+}
+
+static void send_and_submit_pending(struct drbd_device *device, struct list_head *pending)
+{
+	struct blk_plug plug;
+	struct drbd_request *req;
+
+	blk_start_plug(&plug);
+	while ((req = list_first_entry_or_null(pending, struct drbd_request, tl_requests))) {
+		req->rq_state |= RQ_IN_ACT_LOG;
+		req->in_actlog_jif = jiffies;
+		atomic_dec(&device->ap_actlog_cnt);
+		list_del_init(&req->tl_requests);
+		drbd_send_and_submit(device, req);
+	}
+	blk_finish_plug(&plug);
+}
+
+void do_submit(struct work_struct *ws)
+{
+	struct drbd_device *device = container_of(ws, struct drbd_device, submit.worker);
+	LIST_HEAD(incoming);	/* from drbd_make_request() */
+	LIST_HEAD(pending);	/* to be submitted after next AL-transaction commit */
+	LIST_HEAD(busy);	/* blocked by resync requests */
+
+	/* grab new incoming requests */
+	spin_lock_irq(&device->resource->req_lock);
+	list_splice_tail_init(&device->submit.writes, &incoming);
+	spin_unlock_irq(&device->resource->req_lock);
+
+	for (;;) {
+		DEFINE_WAIT(wait);
+
+		/* move used-to-be-busy back to front of incoming */
+		list_splice_init(&busy, &incoming);
+		submit_fast_path(device, &incoming);
+		if (list_empty(&incoming))
+			break;
+
+		for (;;) {
+			prepare_to_wait(&device->al_wait, &wait, TASK_UNINTERRUPTIBLE);
+
+			list_splice_init(&busy, &incoming);
+			prepare_al_transaction_nonblock(device, &incoming, &pending, &busy);
+			if (!list_empty(&pending))
+				break;
+
+			schedule();
+
+			/* If all currently "hot" activity log extents are kept busy by
+			 * incoming requests, we still must not totally starve new
+			 * requests to "cold" extents.
+			 * Something left on &incoming means there had not been
+			 * enough update slots available, and the activity log
+			 * has been marked as "starving".
+			 *
+			 * Try again now, without looking for new requests,
+			 * effectively blocking all new requests until we made
+			 * at least _some_ progress with what we currently have.
+			 */
+			if (!list_empty(&incoming))
+				continue;
+
+			/* Nothing moved to pending, but nothing left
+			 * on incoming: all moved to busy!
+			 * Grab new and iterate. */
+			spin_lock_irq(&device->resource->req_lock);
+			list_splice_tail_init(&device->submit.writes, &incoming);
+			spin_unlock_irq(&device->resource->req_lock);
+		}
+		finish_wait(&device->al_wait, &wait);
+
+		/* If the transaction was full, before all incoming requests
+		 * had been processed, skip ahead to commit, and iterate
+		 * without splicing in more incoming requests from upper layers.
+		 *
+		 * Else, if all incoming have been processed,
+		 * they have become either "pending" (to be submitted after
+		 * next transaction commit) or "busy" (blocked by resync).
+		 *
+		 * Maybe more was queued, while we prepared the transaction?
+		 * Try to stuff those into this transaction as well.
+		 * Be strictly non-blocking here,
+		 * we already have something to commit.
+		 *
+		 * Commit if we don't make any more progres.
+		 */
+
+		while (list_empty(&incoming)) {
+			LIST_HEAD(more_pending);
+			LIST_HEAD(more_incoming);
+			bool made_progress;
+
+			/* It is ok to look outside the lock,
+			 * it's only an optimization anyways */
+			if (list_empty(&device->submit.writes))
+				break;
+
+			spin_lock_irq(&device->resource->req_lock);
+			list_splice_tail_init(&device->submit.writes, &more_incoming);
+			spin_unlock_irq(&device->resource->req_lock);
+
+			if (list_empty(&more_incoming))
+				break;
+
+			made_progress = prepare_al_transaction_nonblock(device, &more_incoming, &more_pending, &busy);
+
+			list_splice_tail_init(&more_pending, &pending);
+			list_splice_tail_init(&more_incoming, &incoming);
+			if (!made_progress)
+				break;
+		}
+
+		drbd_al_begin_io_commit(device);
+		send_and_submit_pending(device, &pending);
+	}
+}
+
+void drbd_submit_bio(struct bio *bio)
+{
+	struct drbd_device *device = bio->bi_bdev->bd_disk->private_data;
+
+	bio = bio_split_to_limits(bio);
+	if (!bio)
+		return;
+
+	/*
+	 * what we "blindly" assume:
+	 */
+	D_ASSERT(device, IS_ALIGNED(bio->bi_iter.bi_size, 512));
+
+	inc_ap_bio(device);
+	__drbd_make_request(device, bio);
+}
+
+static bool net_timeout_reached(struct drbd_request *net_req,
+		struct drbd_connection *connection,
+		unsigned long now, unsigned long ent,
+		unsigned int ko_count, unsigned int timeout)
+{
+	struct drbd_device *device = net_req->device;
+
+	if (!time_after(now, net_req->pre_send_jif + ent))
+		return false;
+
+	if (time_in_range(now, connection->last_reconnect_jif, connection->last_reconnect_jif + ent))
+		return false;
+
+	if (net_req->rq_state & RQ_NET_PENDING) {
+		drbd_warn(device, "Remote failed to finish a request within %ums > ko-count (%u) * timeout (%u * 0.1s)\n",
+			jiffies_to_msecs(now - net_req->pre_send_jif), ko_count, timeout);
+		return true;
+	}
+
+	/* We received an ACK already (or are using protocol A),
+	 * but are waiting for the epoch closing barrier ack.
+	 * Check if we sent the barrier already.  We should not blame the peer
+	 * for being unresponsive, if we did not even ask it yet. */
+	if (net_req->epoch == connection->send.current_epoch_nr) {
+		drbd_warn(device,
+			"We did not send a P_BARRIER for %ums > ko-count (%u) * timeout (%u * 0.1s); drbd kernel thread blocked?\n",
+			jiffies_to_msecs(now - net_req->pre_send_jif), ko_count, timeout);
+		return false;
+	}
+
+	/* Worst case: we may have been blocked for whatever reason, then
+	 * suddenly are able to send a lot of requests (and epoch separating
+	 * barriers) in quick succession.
+	 * The timestamp of the net_req may be much too old and not correspond
+	 * to the sending time of the relevant unack'ed barrier packet, so
+	 * would trigger a spurious timeout.  The latest barrier packet may
+	 * have a too recent timestamp to trigger the timeout, potentially miss
+	 * a timeout.  Right now we don't have a place to conveniently store
+	 * these timestamps.
+	 * But in this particular situation, the application requests are still
+	 * completed to upper layers, DRBD should still "feel" responsive.
+	 * No need yet to kill this connection, it may still recover.
+	 * If not, eventually we will have queued enough into the network for
+	 * us to block. From that point of view, the timestamp of the last sent
+	 * barrier packet is relevant enough.
+	 */
+	if (time_after(now, connection->send.last_sent_barrier_jif + ent)) {
+		drbd_warn(device, "Remote failed to answer a P_BARRIER (sent at %lu jif; now=%lu jif) within %ums > ko-count (%u) * timeout (%u * 0.1s)\n",
+			connection->send.last_sent_barrier_jif, now,
+			jiffies_to_msecs(now - connection->send.last_sent_barrier_jif), ko_count, timeout);
+		return true;
+	}
+	return false;
+}
+
+/* A request is considered timed out, if
+ * - we have some effective timeout from the configuration,
+ *   with some state restrictions applied,
+ * - the oldest request is waiting for a response from the network
+ *   resp. the local disk,
+ * - the oldest request is in fact older than the effective timeout,
+ * - the connection was established (resp. disk was attached)
+ *   for longer than the timeout already.
+ * Note that for 32bit jiffies and very stable connections/disks,
+ * we may have a wrap around, which is catched by
+ *   !time_in_range(now, last_..._jif, last_..._jif + timeout).
+ *
+ * Side effect: once per 32bit wrap-around interval, which means every
+ * ~198 days with 250 HZ, we have a window where the timeout would need
+ * to expire twice (worst case) to become effective. Good enough.
+ */
+
+void request_timer_fn(struct timer_list *t)
+{
+	struct drbd_device *device = from_timer(device, t, request_timer);
+	struct drbd_connection *connection = first_peer_device(device)->connection;
+	struct drbd_request *req_read, *req_write, *req_peer; /* oldest request */
+	struct net_conf *nc;
+	unsigned long oldest_submit_jif;
+	unsigned long ent = 0, dt = 0, et, nt; /* effective timeout = ko_count * timeout */
+	unsigned long now;
+	unsigned int ko_count = 0, timeout = 0;
+
+	rcu_read_lock();
+	nc = rcu_dereference(connection->net_conf);
+	if (nc && device->state.conn >= C_WF_REPORT_PARAMS) {
+		ko_count = nc->ko_count;
+		timeout = nc->timeout;
+	}
+
+	if (get_ldev(device)) { /* implicit state.disk >= D_INCONSISTENT */
+		dt = rcu_dereference(device->ldev->disk_conf)->disk_timeout * HZ / 10;
+		put_ldev(device);
+	}
+	rcu_read_unlock();
+
+
+	ent = timeout * HZ/10 * ko_count;
+	et = min_not_zero(dt, ent);
+
+	if (!et)
+		return; /* Recurring timer stopped */
+
+	now = jiffies;
+	nt = now + et;
+
+	spin_lock_irq(&device->resource->req_lock);
+	req_read = list_first_entry_or_null(&device->pending_completion[0], struct drbd_request, req_pending_local);
+	req_write = list_first_entry_or_null(&device->pending_completion[1], struct drbd_request, req_pending_local);
+
+	/* maybe the oldest request waiting for the peer is in fact still
+	 * blocking in tcp sendmsg.  That's ok, though, that's handled via the
+	 * socket send timeout, requesting a ping, and bumping ko-count in
+	 * we_should_drop_the_connection().
+	 */
+
+	/* check the oldest request we did successfully sent,
+	 * but which is still waiting for an ACK. */
+	req_peer = connection->req_ack_pending;
+
+	/* if we don't have such request (e.g. protocoll A)
+	 * check the oldest requests which is still waiting on its epoch
+	 * closing barrier ack. */
+	if (!req_peer)
+		req_peer = connection->req_not_net_done;
+
+	/* evaluate the oldest peer request only in one timer! */
+	if (req_peer && req_peer->device != device)
+		req_peer = NULL;
+
+	/* do we have something to evaluate? */
+	if (req_peer == NULL && req_write == NULL && req_read == NULL)
+		goto out;
+
+	oldest_submit_jif =
+		(req_write && req_read)
+		? ( time_before(req_write->pre_submit_jif, req_read->pre_submit_jif)
+		  ? req_write->pre_submit_jif : req_read->pre_submit_jif )
+		: req_write ? req_write->pre_submit_jif
+		: req_read ? req_read->pre_submit_jif : now;
+
+	if (ent && req_peer && net_timeout_reached(req_peer, connection, now, ent, ko_count, timeout))
+		_conn_request_state(connection, NS(conn, C_TIMEOUT), CS_VERBOSE | CS_HARD);
+
+	if (dt && oldest_submit_jif != now &&
+		 time_after(now, oldest_submit_jif + dt) &&
+		!time_in_range(now, device->last_reattach_jif, device->last_reattach_jif + dt)) {
+		drbd_warn(device, "Local backing device failed to meet the disk-timeout\n");
+		__drbd_chk_io_error(device, DRBD_FORCE_DETACH);
+	}
+
+	/* Reschedule timer for the nearest not already expired timeout.
+	 * Fallback to now + min(effective network timeout, disk timeout). */
+	ent = (ent && req_peer && time_before(now, req_peer->pre_send_jif + ent))
+		? req_peer->pre_send_jif + ent : now + et;
+	dt = (dt && oldest_submit_jif != now && time_before(now, oldest_submit_jif + dt))
+		? oldest_submit_jif + dt : now + et;
+	nt = time_before(ent, dt) ? ent : dt;
+out:
+	spin_unlock_irq(&device->resource->req_lock);
+	mod_timer(&device->request_timer, nt);
+}