Merge tag 'for-linus-20190726' of git://git.kernel.dk/linux-block

Pull block fixes from Jens Axboe:

 - Several io_uring fixes/improvements:
     - Blocking fix for O_DIRECT (me)
     - Latter page slowness for registered buffers (me)
     - Fix poll hang under certain conditions (me)
     - Defer sequence check fix for wrapped rings (Zhengyuan)
     - Mismatch in async inc/dec accounting (Zhengyuan)
     - Memory ordering issue that could cause stall (Zhengyuan)
      - Track sequential defer in bytes, not pages (Zhengyuan)

 - NVMe pull request from Christoph

 - Set of hang fixes for wbt (Josef)

 - Redundant error message kill for libahci (Ding)

 - Remove unused blk_mq_sched_started_request() and related ops (Marcos)

 - drbd dynamic alloc shash descriptor to reduce stack use (Arnd)

 - blkcg ->pd_stat() non-debug print (Tejun)

 - bcache memory leak fix (Wei)

 - Comment fix (Akinobu)

 - BFQ perf regression fix (Paolo)

* tag 'for-linus-20190726' of git://git.kernel.dk/linux-block: (24 commits)
  io_uring: ensure ->list is initialized for poll commands
  Revert "nvme-pci: don't create a read hctx mapping without read queues"
  nvme: fix multipath crash when ANA is deactivated
  nvme: fix memory leak caused by incorrect subsystem free
  nvme: ignore subnqn for ADATA SX6000LNP
  drbd: dynamically allocate shash descriptor
  block: blk-mq: Remove blk_mq_sched_started_request and started_request
  bcache: fix possible memory leak in bch_cached_dev_run()
  io_uring: track io length in async_list based on bytes
  io_uring: don't use iov_iter_advance() for fixed buffers
  block: properly handle IOCB_NOWAIT for async O_DIRECT IO
  blk-mq: allow REQ_NOWAIT to return an error inline
  io_uring: add a memory barrier before atomic_read
  rq-qos: use a mb for got_token
  rq-qos: set ourself TASK_UNINTERRUPTIBLE after we schedule
  rq-qos: don't reset has_sleepers on spurious wakeups
  rq-qos: fix missed wake-ups in rq_qos_throttle
  wait: add wq_has_single_sleeper helper
  block, bfq: check also in-flight I/O in dispatch plugging
  block: fix sysfs module parameters directory path in comment
  ...

7 files changed, 62 insertions, 45 deletions

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 72860325245a..586fcfe227ea 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -3354,38 +3354,57 @@ static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
  * there is no active group, then the primary expectation for
  * this device is probably a high throughput.
  *
- * We are now left only with explaining the additional
- * compound condition that is checked below for deciding
- * whether the scenario is asymmetric. To explain this
- * compound condition, we need to add that the function
+ * We are now left only with explaining the two sub-conditions in the
+ * additional compound condition that is checked below for deciding
+ * whether the scenario is asymmetric. To explain the first
+ * sub-condition, we need to add that the function
  * bfq_asymmetric_scenario checks the weights of only
- * non-weight-raised queues, for efficiency reasons (see
- * comments on bfq_weights_tree_add()). Then the fact that
- * 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 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.
+ * non-weight-raised queues, for efficiency reasons (see comments on
+ * bfq_weights_tree_add()). Then the fact that 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 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.
+ *
+ * The second sub-condition checked in the compound condition is
+ * whether there is a fair amount of already in-flight I/O not
+ * belonging to bfqq. If so, I/O dispatching is to be plugged, for the
+ * following reason. The drive may decide to serve in-flight
+ * non-bfqq's I/O requests before bfqq's ones, thereby delaying the
+ * arrival of new I/O requests for bfqq (recall that bfqq is sync). If
+ * I/O-dispatching is not plugged, then, while bfqq remains empty, a
+ * basically uncontrolled amount of I/O from other queues may be
+ * dispatched too, possibly causing the service of bfqq's I/O to be
+ * delayed even longer in the drive. This problem gets more and more
+ * serious as the speed and the queue depth of the drive grow,
+ * because, as these two quantities grow, the probability to find no
+ * queue busy but many requests in flight grows too. By contrast,
+ * plugging I/O dispatching minimizes the delay induced by already
+ * in-flight I/O, and enables bfqq to recover the bandwidth it may
+ * lose because of this delay.
  *
  * As a side note, it is worth considering that the above
- * device-idling countermeasures may however fail in the
- * following unlucky scenario: if idling is (correctly)
- * disabled in a time period during which all symmetry
- * sub-conditions hold, and hence the device is allowed to
- * enqueue many requests, but at some later point in time some
- * sub-condition stops to hold, then it may become impossible
- * to let requests be served in the desired order until all
- * the requests already queued in the device have been served.
+ * device-idling countermeasures may however fail in the following
+ * unlucky scenario: if I/O-dispatch plugging is (correctly) disabled
+ * in a time period during which all symmetry sub-conditions hold, and
+ * therefore the device is allowed to enqueue many requests, but at
+ * some later point in time some sub-condition stops to hold, then it
+ * may become impossible to make requests be served in the desired
+ * order until all the requests already queued in the device have been
+ * served. The last sub-condition commented above somewhat mitigates
+ * this problem for weight-raised queues.
  */
 static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd,
 						 struct bfq_queue *bfqq)
 {
 	return (bfqq->wr_coeff > 1 &&
-		bfqd->wr_busy_queues <
-		bfq_tot_busy_queues(bfqd)) ||
+		(bfqd->wr_busy_queues <
+		 bfq_tot_busy_queues(bfqd) ||
+		 bfqd->rq_in_driver >=
+		 bfqq->dispatched + 4)) ||
 		bfq_asymmetric_scenario(bfqd, bfqq);
 }
 
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 24ed26957367..55a7dc227dfb 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -54,7 +54,7 @@ static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
 
 static LIST_HEAD(all_blkcgs);		/* protected by blkcg_pol_mutex */
 
-static bool blkcg_debug_stats = false;
+bool blkcg_debug_stats = false;
 static struct workqueue_struct *blkcg_punt_bio_wq;
 
 static bool blkcg_policy_enabled(struct request_queue *q,
@@ -944,10 +944,7 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)
 					 dbytes, dios);
 		}
 
-		if (!blkcg_debug_stats)
-			goto next;
-
-		if (atomic_read(&blkg->use_delay)) {
+		if (blkcg_debug_stats && atomic_read(&blkg->use_delay)) {
 			has_stats = true;
 			off += scnprintf(buf+off, size-off,
 					 " use_delay=%d delay_nsec=%llu",
@@ -967,7 +964,7 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)
 				has_stats = true;
 			off += written;
 		}
-next:
+
 		if (has_stats) {
 			if (off < size - 1) {
 				off += scnprintf(buf+off, size-off, "\n");
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index d973c38ee4fd..0fff7b56df0e 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -917,6 +917,9 @@ static size_t iolatency_pd_stat(struct blkg_policy_data *pd, char *buf,
 	unsigned long long avg_lat;
 	unsigned long long cur_win;
 
+	if (!blkcg_debug_stats)
+		return 0;
+
 	if (iolat->ssd)
 		return iolatency_ssd_stat(iolat, buf, size);
 
diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index cf22ab00fefb..126021fc3a11 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -61,15 +61,6 @@ static inline void blk_mq_sched_completed_request(struct request *rq, u64 now)
 		e->type->ops.completed_request(rq, now);
 }
 
-static inline void blk_mq_sched_started_request(struct request *rq)
-{
-	struct request_queue *q = rq->q;
-	struct elevator_queue *e = q->elevator;
-
-	if (e && e->type->ops.started_request)
-		e->type->ops.started_request(rq);
-}
-
 static inline void blk_mq_sched_requeue_request(struct request *rq)
 {
 	struct request_queue *q = rq->q;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index b038ec680e84..f78d3287dd82 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -669,8 +669,6 @@ void blk_mq_start_request(struct request *rq)
 {
 	struct request_queue *q = rq->q;
 
-	blk_mq_sched_started_request(rq);
-
 	trace_block_rq_issue(q, rq);
 
 	if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) {
@@ -1960,9 +1958,13 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 	rq = blk_mq_get_request(q, bio, &data);
 	if (unlikely(!rq)) {
 		rq_qos_cleanup(q, bio);
-		if (bio->bi_opf & REQ_NOWAIT)
+
+		cookie = BLK_QC_T_NONE;
+		if (bio->bi_opf & REQ_NOWAIT_INLINE)
+			cookie = BLK_QC_T_EAGAIN;
+		else if (bio->bi_opf & REQ_NOWAIT)
 			bio_wouldblock_error(bio);
-		return BLK_QC_T_NONE;
+		return cookie;
 	}
 
 	trace_block_getrq(q, bio, bio->bi_opf);
diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
index 659ccb8b693f..3954c0dc1443 100644
--- a/block/blk-rq-qos.c
+++ b/block/blk-rq-qos.c
@@ -202,6 +202,7 @@ static int rq_qos_wake_function(struct wait_queue_entry *curr,
 		return -1;
 
 	data->got_token = true;
+	smp_wmb();
 	list_del_init(&curr->entry);
 	wake_up_process(data->task);
 	return 1;
@@ -244,7 +245,9 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data,
 		return;
 
 	prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE);
+	has_sleeper = !wq_has_single_sleeper(&rqw->wait);
 	do {
+		/* The memory barrier in set_task_state saves us here. */
 		if (data.got_token)
 			break;
 		if (!has_sleeper && acquire_inflight_cb(rqw, private_data)) {
@@ -255,12 +258,14 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data,
 			 * which means we now have two. Put our local token
 			 * and wake anyone else potentially waiting for one.
 			 */
+			smp_rmb();
 			if (data.got_token)
 				cleanup_cb(rqw, private_data);
 			break;
 		}
 		io_schedule();
-		has_sleeper = false;
+		has_sleeper = true;
+		set_current_state(TASK_UNINTERRUPTIBLE);
 	} while (1);
 	finish_wait(&rqw->wait, &data.wq);
 }
diff --git a/block/genhd.c b/block/genhd.c
index 97887e59f3b2..54f1f0d381f4 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1969,7 +1969,7 @@ static const struct attribute *disk_events_attrs[] = {
  * The default polling interval can be specified by the kernel
  * parameter block.events_dfl_poll_msecs which defaults to 0
  * (disable).  This can also be modified runtime by writing to
- * /sys/module/block/events_dfl_poll_msecs.
+ * /sys/module/block/parameters/events_dfl_poll_msecs.
  */
 static int disk_events_set_dfl_poll_msecs(const char *val,
 					  const struct kernel_param *kp)