Merge tag 'v4.20-rc6' into for-4.21/block

Pull in v4.20-rc6 to resolve the conflict in NVMe, but also to get the
two corruption fixes. We're going to be overhauling the direct dispatch
path, and we need to do that on top of the changes we made for that
in mainline.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

4 files changed, 111 insertions, 28 deletions

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 3d1f319fe977..cd307767a134 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -638,7 +638,7 @@ static bool bfq_varied_queue_weights_or_active_groups(struct bfq_data *bfqd)
 		 bfqd->queue_weights_tree.rb_node->rb_right)
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
 	       ) ||
-		(bfqd->num_active_groups > 0
+		(bfqd->num_groups_with_pending_reqs > 0
 #endif
 	       );
 }
@@ -802,7 +802,21 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
 			 */
 			break;
 		}
-		bfqd->num_active_groups--;
+
+		/*
+		 * The decrement of num_groups_with_pending_reqs is
+		 * not performed immediately upon the deactivation of
+		 * entity, but it is delayed to when it also happens
+		 * that the first leaf descendant bfqq of entity gets
+		 * all its pending requests completed. The following
+		 * instructions perform this delayed decrement, if
+		 * needed. See the comments on
+		 * num_groups_with_pending_reqs for details.
+		 */
+		if (entity->in_groups_with_pending_reqs) {
+			entity->in_groups_with_pending_reqs = false;
+			bfqd->num_groups_with_pending_reqs--;
+		}
 	}
 }
 
@@ -3529,27 +3543,44 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq)
 	 * fact, if there are active groups, then, for condition (i)
 	 * to become false, it is enough that an active group contains
 	 * more active processes or sub-groups than some other active
-	 * group. We address this issue with the following bi-modal
-	 * behavior, implemented in the function
+	 * group. More precisely, for condition (i) to hold because of
+	 * such a group, it is not even necessary that the group is
+	 * (still) active: it is sufficient that, even if the group
+	 * has become inactive, some of its descendant processes still
+	 * have some request already dispatched but still waiting for
+	 * completion. In fact, requests have still to be guaranteed
+	 * their share of the throughput even after being
+	 * dispatched. In this respect, it is easy to show that, if a
+	 * group frequently becomes inactive while still having
+	 * in-flight requests, and if, when this happens, the group is
+	 * not considered in the calculation of whether the scenario
+	 * is asymmetric, then the group may fail to be guaranteed its
+	 * fair share of the throughput (basically because idling may
+	 * not be performed for the descendant processes of the group,
+	 * but it had to be).  We address this issue with the
+	 * following bi-modal behavior, implemented in the function
 	 * bfq_symmetric_scenario().
 	 *
-	 * If there are active groups, then the scenario is tagged as
+	 * If there are groups with requests waiting for completion
+	 * (as commented above, some of these groups may even be
+	 * already inactive), then the scenario is tagged as
 	 * asymmetric, conservatively, without checking any of the
 	 * conditions (i) and (ii). So the device is idled for bfqq.
 	 * This behavior matches also the fact that groups are created
-	 * exactly if controlling I/O (to preserve bandwidth and
-	 * latency guarantees) is a primary concern.
+	 * exactly if controlling I/O is a primary concern (to
+	 * preserve bandwidth and latency guarantees).
 	 *
-	 * On the opposite end, if there are no active groups, then
-	 * only condition (i) is actually controlled, i.e., provided
-	 * that condition (i) holds, idling is not performed,
-	 * regardless of whether condition (ii) holds. In other words,
-	 * only if condition (i) does not hold, then idling is
-	 * allowed, and the device tends to be prevented from queueing
-	 * many requests, possibly of several processes. Since there
-	 * are no active groups, then, to control condition (i) it is
-	 * enough to check whether all active queues have the same
-	 * weight.
+	 * On the opposite end, if there are no groups with requests
+	 * waiting for completion, then only condition (i) is actually
+	 * controlled, i.e., provided that condition (i) holds, idling
+	 * is not performed, regardless of whether condition (ii)
+	 * holds. In other words, only if condition (i) does not hold,
+	 * then idling is allowed, and the device tends to be
+	 * prevented from queueing many requests, possibly of several
+	 * processes. Since there are no groups with requests waiting
+	 * for completion, then, to control condition (i) it is enough
+	 * to check just whether all the queues with requests waiting
+	 * for completion also have the same weight.
 	 *
 	 * Not checking condition (ii) evidently exposes bfqq to the
 	 * risk of getting less throughput than its fair share.
@@ -3607,10 +3638,11 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq)
 	 * bfqq is weight-raised is checked explicitly here. More
 	 * precisely, the compound condition below takes into account
 	 * also the fact that, even if bfqq is being weight-raised,
-	 * the scenario is still symmetric if all active queues happen
-	 * to be weight-raised. Actually, we should be even more
-	 * precise here, and differentiate between interactive weight
-	 * raising and soft real-time weight raising.
+	 * the scenario is still symmetric if all queues with requests
+	 * waiting for completion happen to be
+	 * weight-raised. Actually, we should be even more precise
+	 * here, and differentiate between interactive weight raising
+	 * and soft real-time weight raising.
 	 *
 	 * As a side note, it is worth considering that the above
 	 * device-idling countermeasures may however fail in the
@@ -5417,7 +5449,7 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 	bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
 
 	bfqd->queue_weights_tree = RB_ROOT;
-	bfqd->num_active_groups = 0;
+	bfqd->num_groups_with_pending_reqs = 0;
 
 	INIT_LIST_HEAD(&bfqd->active_list);
 	INIT_LIST_HEAD(&bfqd->idle_list);
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 77651d817ecd..0b02bf302de0 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -196,6 +196,9 @@ struct bfq_entity {
 
 	/* flag, set to request a weight, ioprio or ioprio_class change  */
 	int prio_changed;
+
+	/* flag, set if the entity is counted in groups_with_pending_reqs */
+	bool in_groups_with_pending_reqs;
 };
 
 struct bfq_group;
@@ -448,10 +451,54 @@ struct bfq_data {
 	 * bfq_weights_tree_[add|remove] for further details).
 	 */
 	struct rb_root queue_weights_tree;
+
 	/*
-	 * number of groups with requests still waiting for completion
+	 * Number of groups with at least one descendant process that
+	 * has at least one request waiting for completion. Note that
+	 * this accounts for also requests already dispatched, but not
+	 * yet completed. Therefore this number of groups may differ
+	 * (be larger) than the number of active groups, as a group is
+	 * considered active only if its corresponding entity has
+	 * descendant queues with at least one request queued. This
+	 * number is used to decide whether a scenario is symmetric.
+	 * For a detailed explanation see comments on the computation
+	 * of the variable asymmetric_scenario in the function
+	 * bfq_better_to_idle().
+	 *
+	 * However, it is hard to compute this number exactly, for
+	 * groups with multiple descendant processes. Consider a group
+	 * that is inactive, i.e., that has no descendant process with
+	 * pending I/O inside BFQ queues. Then suppose that
+	 * num_groups_with_pending_reqs is still accounting for this
+	 * group, because the group has descendant processes with some
+	 * I/O request still in flight. num_groups_with_pending_reqs
+	 * should be decremented when the in-flight request of the
+	 * last descendant process is finally completed (assuming that
+	 * nothing else has changed for the group in the meantime, in
+	 * terms of composition of the group and active/inactive state of child
+	 * groups and processes). To accomplish this, an additional
+	 * pending-request counter must be added to entities, and must
+	 * be updated correctly. To avoid this additional field and operations,
+	 * we resort to the following tradeoff between simplicity and
+	 * accuracy: for an inactive group that is still counted in
+	 * num_groups_with_pending_reqs, we decrement
+	 * num_groups_with_pending_reqs when the first descendant
+	 * process of the group remains with no request waiting for
+	 * completion.
+	 *
+	 * Even this simpler decrement strategy requires a little
+	 * carefulness: to avoid multiple decrements, we flag a group,
+	 * more precisely an entity representing a group, as still
+	 * counted in num_groups_with_pending_reqs when it becomes
+	 * inactive. Then, when the first descendant queue of the
+	 * entity remains with no request waiting for completion,
+	 * num_groups_with_pending_reqs is decremented, and this flag
+	 * is reset. After this flag is reset for the entity,
+	 * num_groups_with_pending_reqs won't be decremented any
+	 * longer in case a new descendant queue of the entity remains
+	 * with no request waiting for completion.
 	 */
-	unsigned int num_active_groups;
+	unsigned int num_groups_with_pending_reqs;
 
 	/*
 	 * Number of bfq_queues containing requests (including the
diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index 4b0d5fb69160..63e0f12be7c9 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -1012,7 +1012,10 @@ static void __bfq_activate_entity(struct bfq_entity *entity,
 			container_of(entity, struct bfq_group, entity);
 		struct bfq_data *bfqd = bfqg->bfqd;
 
-		bfqd->num_active_groups++;
+		if (!entity->in_groups_with_pending_reqs) {
+			entity->in_groups_with_pending_reqs = true;
+			bfqd->num_groups_with_pending_reqs++;
+		}
 	}
 #endif
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7f478ae288af..b645275dfe5f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1831,7 +1831,7 @@ insert:
 	if (bypass_insert)
 		return BLK_STS_RESOURCE;
 
-	blk_mq_sched_insert_request(rq, false, run_queue, false);
+	blk_mq_request_bypass_insert(rq, run_queue);
 	return BLK_STS_OK;
 }
 
@@ -1847,7 +1847,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 
 	ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false, true);
 	if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
-		blk_mq_sched_insert_request(rq, false, true, false);
+		blk_mq_request_bypass_insert(rq, true);
 	else if (ret != BLK_STS_OK)
 		blk_mq_end_request(rq, ret);
 
@@ -1881,7 +1881,8 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
 		if (ret != BLK_STS_OK) {
 			if (ret == BLK_STS_RESOURCE ||
 					ret == BLK_STS_DEV_RESOURCE) {
-				list_add(&rq->queuelist, list);
+				blk_mq_request_bypass_insert(rq,
+							list_empty(list));
 				break;
 			}
 			blk_mq_end_request(rq, ret);