On Thu, Nov 30, 2017 at 04:08:47PM -0800, Bart Van Assche wrote:

During request dispatch, after a scheduler or per-CPU queue has been examined, .put_budget() is called if the examined queue is empty. Since a new request may be queued concurrently with the .put_budget() call, a request queue needs to be rerun after each .put_budget() call.

If a request is queued concurrently from another path, it can be run from that path, so don't need to rerun in __blk_mq_run_hw_queue().

Fixes: commit 1f460b63d4b3 ("blk-mq: don't restart queue when .get_budget returns BLK_STS_RESOURCE") Signed-off-by: Bart Van Assche bart.vanassche@wdc.com Cc: Ming Lei ming.lei@redhat.com Cc: Omar Sandoval osandov@fb.com Cc: Christoph Hellwig hch@lst.de Cc: Hannes Reinecke hare@suse.de Cc: Johannes Thumshirn jthumshirn@suse.de Cc: stable@vger.kernel.org

---

block/blk-mq-sched.c | 39 ++++++++++++++++++++------------------- block/blk-mq-sched.h | 2 +- block/blk-mq.c | 17 ++++++++++++----- 3 files changed, 33 insertions(+), 25 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 398545d94521..3a935081a2d3 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -82,12 +82,8 @@ static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx) return blk_mq_run_hw_queue(hctx, true); } -/*

• • 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) +/* returns true if hctx needs to be run again */ +static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) { struct request_queue *q = hctx->queue; struct elevator_queue *e = q->elevator; @@ -106,7 +102,7 @@ static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) rq = e->type->ops.mq.dispatch_request(hctx); if (!rq) { blk_mq_put_dispatch_budget(hctx);

• 	break;
  

• 	return true;
  

  }

/* @@ -116,6 +112,8 @@ static void 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, @@ -129,16 +127,13 @@ static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx, return hctx->ctxs[idx]; } -/*

• • 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) +/* returns true if hctx needs to be run again */ +static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) { struct request_queue *q = hctx->queue; LIST_HEAD(rq_list); struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);

• bool ret = false;

do { struct request *rq; @@ -152,6 +147,7 @@ static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) rq = blk_mq_dequeue_from_ctx(hctx, ctx); if (!rq) { blk_mq_put_dispatch_budget(hctx);

• 	ret = true;
  break;
  

  }

@@ -168,19 +164,22 @@ static void 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 ret;

} /* return true if hw queue need to be run again */ -void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) +bool 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;
  

• return false;
  

hctx->run++; @@ -212,12 +211,12 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) if (!list_empty(&rq_list)) { if (blk_mq_dispatch_rq_list(q, &rq_list, false)) { if (has_sched_dispatch)

• 		blk_mq_do_dispatch_sched(hctx);
  

• 		run_queue = blk_mq_do_dispatch_sched(hctx);
  else
  

• 		blk_mq_do_dispatch_ctx(hctx);
  

• 		run_queue = blk_mq_do_dispatch_ctx(hctx);
  

  } } else if (has_sched_dispatch) {

• blk_mq_do_dispatch_sched(hctx);
  

• run_queue = blk_mq_do_dispatch_sched(hctx);
  

  } else if (q->mq_ops->get_budget) { /*
  • If we need to get budget before queuing request, we

@@ -227,11 +226,13 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) * TODO: get more budgets, and dequeue more requests in * one time. */

• blk_mq_do_dispatch_ctx(hctx);
  

• run_queue = blk_mq_do_dispatch_ctx(hctx);
  

  } else { blk_mq_flush_busy_ctxs(hctx, &rq_list); blk_mq_dispatch_rq_list(q, &rq_list, false); }
• return run_queue;

} bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio, diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h index ba1d1418a96d..1ccfb8027cfc 100644 --- a/block/blk-mq-sched.h +++ b/block/blk-mq-sched.h @@ -23,7 +23,7 @@ void blk_mq_sched_insert_requests(struct request_queue *q, struct blk_mq_ctx *ctx, struct list_head *list, bool run_queue_async); -void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx); +bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx); int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e); void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e); diff --git a/block/blk-mq.c b/block/blk-mq.c index 3e0ce940377f..b4225f606737 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1079,7 +1079,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, { struct blk_mq_hw_ctx *hctx; struct request *rq, *nxt;

• bool no_tag = false;

• bool restart = false, no_tag = false; int errors, queued;

if (list_empty(list)) @@ -1105,8 +1105,10 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, * we'll re-run it below. */ if (!blk_mq_mark_tag_wait(&hctx, rq)) {

• 		if (got_budget)
  

• 		if (got_budget) {
  		blk_mq_put_dispatch_budget(hctx);
  

• 			restart = true;
  

• 		}
  	/*
  	 * For non-shared tags, the RESTART check
  	 * will suffice.
  

@@ -1193,7 +1195,8 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, * returning BLK_STS_RESOURCE. Two exceptions are scsi-mq * and dm-rq. */

• if (!blk_mq_sched_needs_restart(hctx) ||
  

• if (restart ||
  

•     !blk_mq_sched_needs_restart(hctx) ||
  

  (no_tag && list_empty_careful(&hctx->dispatch_wait.entry))) blk_mq_run_hw_queue(hctx, true); }

@@ -1204,6 +1207,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) { int srcu_idx;

• bool run_queue;

/* * We should be running this queue from one of the CPUs that @@ -1220,15 +1224,18 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) if (!(hctx->flags & BLK_MQ_F_BLOCKING)) { rcu_read_lock();

• blk_mq_sched_dispatch_requests(hctx);
  

• run_queue = blk_mq_sched_dispatch_requests(hctx);
  

  rcu_read_unlock(); } else { might_sleep();

srcu_idx = srcu_read_lock(hctx->queue_rq_srcu);

• blk_mq_sched_dispatch_requests(hctx);
  

• run_queue = blk_mq_sched_dispatch_requests(hctx);
  

  srcu_read_unlock(hctx->queue_rq_srcu, srcu_idx); }
• if (run_queue)

• blk_mq_sched_restart(hctx);
  

} /* -- 2.15.0