Merge tag 'for-linus-20180825' of git://git.kernel.dk/linux-block

Pull block fixes from Jens Axboe:
 "A few small fixes for this merge window:

   - Locking imbalance fix for bcache (Shan Hai)

   - A few small fixes for wbt. One is a cleanup/prep, one is a fix for
     an existing issue, and the last two are fixes for changes that went
     into this merge window (me)"

* tag 'for-linus-20180825' of git://git.kernel.dk/linux-block:
  blk-wbt: don't maintain inflight counts if disabled
  blk-wbt: fix has-sleeper queueing check
  blk-wbt: use wq_has_sleeper() for wq active check
  blk-wbt: move disable check into get_limit()
  bcache: release dc->writeback_lock properly in bch_writeback_thread()

3 files changed, 38 insertions, 22 deletions

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index bb109bb0a055..3772671cf2bc 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -453,9 +453,26 @@ static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,
         else if (val >= 0)
                 val *= 1000ULL;
 
-        wbt_set_min_lat(q, val);
+        /*
+         * Ensure that the queue is idled, in case the latency update
+         * ends up either enabling or disabling wbt completely. We can't
+         * have IO inflight if that happens.
+         */
+        if (q->mq_ops) {
+                blk_mq_freeze_queue(q);
+                blk_mq_quiesce_queue(q);
+        } else
+                blk_queue_bypass_start(q);
 
+        wbt_set_min_lat(q, val);
         wbt_update_limits(q);
+
+        if (q->mq_ops) {
+                blk_mq_unquiesce_queue(q);
+                blk_mq_unfreeze_queue(q);
+        } else
+                blk_queue_bypass_end(q);
+
         return count;
 }
 
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index bb93c7c2b182..84507d3e9a98 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -118,7 +118,7 @@ static void rwb_wake_all(struct rq_wb *rwb)
         for (i = 0; i < WBT_NUM_RWQ; i++) {
                 struct rq_wait *rqw = &rwb->rq_wait[i];
 
-                if (waitqueue_active(&rqw->wait))
+                if (wq_has_sleeper(&rqw->wait))
                         wake_up_all(&rqw->wait);
         }
 }
@@ -162,7 +162,7 @@ static void __wbt_done(struct rq_qos *rqos, enum wbt_flags wb_acct)
         if (inflight && inflight >= limit)
                 return;
 
-        if (waitqueue_active(&rqw->wait)) {
+        if (wq_has_sleeper(&rqw->wait)) {
                 int diff = limit - inflight;
 
                 if (!inflight || diff >= rwb->wb_background / 2)
@@ -449,6 +449,13 @@ static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw)
 {
         unsigned int limit;
 
+        /*
+         * If we got disabled, just return UINT_MAX. This ensures that
+         * we'll properly inc a new IO, and dec+wakeup at the end.
+         */
+        if (!rwb_enabled(rwb))
+                return UINT_MAX;
+
         if ((rw & REQ_OP_MASK) == REQ_OP_DISCARD)
                 return rwb->wb_background;
 
@@ -485,31 +492,17 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
 {
         struct rq_wait *rqw = get_rq_wait(rwb, wb_acct);
         DECLARE_WAITQUEUE(wait, current);
+        bool has_sleeper;
 
-        /*
-        * inc it here even if disabled, since we'll dec it at completion.
-        * this only happens if the task was sleeping in __wbt_wait(),
-        * and someone turned it off at the same time.
-        */
-        if (!rwb_enabled(rwb)) {
-                atomic_inc(&rqw->inflight);
-                return;
-        }
-
-        if (!waitqueue_active(&rqw->wait)
-                && rq_wait_inc_below(rqw, get_limit(rwb, rw)))
+        has_sleeper = wq_has_sleeper(&rqw->wait);
+        if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw)))
                 return;
 
         add_wait_queue_exclusive(&rqw->wait, &wait);
         do {
                 set_current_state(TASK_UNINTERRUPTIBLE);
 
-                if (!rwb_enabled(rwb)) {
-                        atomic_inc(&rqw->inflight);
-                        break;
-                }
-
-                if (rq_wait_inc_below(rqw, get_limit(rwb, rw)))
+                if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw)))
                         break;
 
                 if (lock) {
@@ -518,6 +511,7 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
                         spin_lock_irq(lock);
                 } else
                         io_schedule();
+                has_sleeper = false;
         } while (1);
 
         __set_current_state(TASK_RUNNING);
@@ -546,6 +540,9 @@ static enum wbt_flags bio_to_wbt_flags(struct rq_wb *rwb, struct bio *bio)
 {
         enum wbt_flags flags = 0;
 
+        if (!rwb_enabled(rwb))
+                return 0;
+
         if (bio_op(bio) == REQ_OP_READ) {
                 flags = WBT_READ;
         } else if (wbt_should_throttle(rwb, bio)) {
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 6be05bd7ca67..08c3a9f9676c 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -685,8 +685,10 @@ static int bch_writeback_thread(void *arg)
                          * data on cache. BCACHE_DEV_DETACHING flag is set in
                          * bch_cached_dev_detach().
                          */
-                        if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
+                        if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags)) {
+                                up_write(&dc->writeback_lock);
                                 break;
+                        }
                 }
 
                 up_write(&dc->writeback_lock);