blk-mq: don't restart queue when .get_budget returns BLK_STS_RESOURCE

SCSI restarts its queue in scsi_end_request() automatically, so we don't
need to handle this case in blk-mq.

Especailly any request won't be dequeued in this case, we needn't to
worry about IO hang caused by restart vs. dispatch.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 20 insertions, 25 deletions

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index daab27feb653..7775f6b12fa9 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -81,8 +81,12 @@ void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
         }
 }
 
-/* return true if hctx need to run again */
-static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
+/*
+ * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
+ * its queue by itself in its completion handler, so we don't need to
+ * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
+ */
+static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 {
         struct request_queue *q = hctx->queue;
         struct elevator_queue *e = q->elevator;
@@ -98,7 +102,7 @@ static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 
                 ret = blk_mq_get_dispatch_budget(hctx);
                 if (ret == BLK_STS_RESOURCE)
-                        return true;
+                        break;
 
                 rq = e->type->ops.mq.dispatch_request(hctx);
                 if (!rq) {
@@ -116,8 +120,6 @@ static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
                  */
                 list_add(&rq->queuelist, &rq_list);
         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
-
-        return false;
 }
 
 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
@@ -131,8 +133,12 @@ static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
         return hctx->ctxs[idx];
 }
 
-/* return true if hctx need to run again */
-static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
+/*
+ * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
+ * its queue by itself in its completion handler, so we don't need to
+ * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
+ */
+static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 {
         struct request_queue *q = hctx->queue;
         LIST_HEAD(rq_list);
@@ -147,7 +153,7 @@ static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 
                 ret = blk_mq_get_dispatch_budget(hctx);
                 if (ret == BLK_STS_RESOURCE)
-                        return true;
+                        break;
 
                 rq = blk_mq_dequeue_from_ctx(hctx, ctx);
                 if (!rq) {
@@ -171,22 +177,19 @@ static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 
         WRITE_ONCE(hctx->dispatch_from, ctx);
-
-        return false;
 }
 
 /* return true if hw queue need to be run again */
-bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
+void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 {
         struct request_queue *q = hctx->queue;
         struct elevator_queue *e = q->elevator;
         const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
         LIST_HEAD(rq_list);
-        bool run_queue = false;
 
         /* RCU or SRCU read lock is needed before checking quiesced flag */
         if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
-                return false;
+                return;
 
         hctx->run++;
 
@@ -218,12 +221,12 @@ bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
                 blk_mq_sched_mark_restart_hctx(hctx);
                 if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
                         if (has_sched_dispatch)
-                                run_queue = blk_mq_do_dispatch_sched(hctx);
+                                blk_mq_do_dispatch_sched(hctx);
                         else
-                                run_queue = blk_mq_do_dispatch_ctx(hctx);
+                                blk_mq_do_dispatch_ctx(hctx);
                 }
         } else if (has_sched_dispatch) {
-                run_queue = blk_mq_do_dispatch_sched(hctx);
+                blk_mq_do_dispatch_sched(hctx);
         } else if (q->mq_ops->get_budget) {
                 /*
                  * If we need to get budget before queuing request, we
@@ -233,19 +236,11 @@ bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
                  * TODO: get more budgets, and dequeue more requests in
                  * one time.
                  */
-                run_queue = blk_mq_do_dispatch_ctx(hctx);
+                blk_mq_do_dispatch_ctx(hctx);
         } else {
                 blk_mq_flush_busy_ctxs(hctx, &rq_list);
                 blk_mq_dispatch_rq_list(q, &rq_list, false);
         }
-
-        if (run_queue && !blk_mq_sched_needs_restart(hctx) &&
-                        !test_bit(BLK_MQ_S_TAG_WAITING, &hctx->state)) {
-                blk_mq_sched_mark_restart_hctx(hctx);
-                return true;
-        }
-
-        return false;
 }
 
 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,