[PATCH] block: Submit flush requests to the I/O scheduler

[Bart Van Assche <bvanassche@acm.org>]

When submitting a REQ_OP_WRITE | REQ_FUA request to a zoned storage
device, these requests must be passed to the (mq-deadline) I/O scheduler
to ensure that these happen at the write pointer. It has been verfied
that this patch prevents that write pointer violations happen
sporadically when f2fs is using a zoned storage device.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/blk-mq.c | 31 ++++---------------------------
 1 file changed, 4 insertions(+), 27 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 5ee62b95f3e5..530aad95cc33 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2546,16 +2546,14 @@ static blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
 	return __blk_mq_try_issue_directly(rq->mq_hctx, rq, true, last);
 }
 
-static void blk_mq_plug_issue_direct(struct blk_plug *plug, bool from_schedule)
+static void blk_mq_plug_issue(struct blk_plug *plug, bool from_schedule)
 {
 	struct blk_mq_hw_ctx *hctx = NULL;
 	struct request *rq;
 	int queued = 0;
-	int errors = 0;
 
 	while ((rq = rq_list_pop(&plug->mq_list))) {
 		bool last = rq_list_empty(plug->mq_list);
-		blk_status_t ret;
 
 		if (hctx != rq->mq_hctx) {
 			if (hctx)
@@ -2563,29 +2561,9 @@ static void blk_mq_plug_issue_direct(struct blk_plug *plug, bool from_schedule)
 			hctx = rq->mq_hctx;
 		}
 
-		ret = blk_mq_request_issue_directly(rq, last);
-		switch (ret) {
-		case BLK_STS_OK:
-			queued++;
-			break;
-		case BLK_STS_RESOURCE:
-		case BLK_STS_DEV_RESOURCE:
-			blk_mq_request_bypass_insert(rq, false, last);
-			blk_mq_commit_rqs(hctx, &queued, from_schedule);
-			return;
-		default:
-			blk_mq_end_request(rq, ret);
-			errors++;
-			break;
-		}
+		blk_mq_sched_insert_request(rq, /*at_head=*/false,
+			/*run_queue=*/last, /*async=*/false);
 	}
-
-	/*
-	 * If we didn't flush the entire list, we could have told the driver
-	 * there was more coming, but that turned out to be a lie.
-	 */
-	if (errors)
-		blk_mq_commit_rqs(hctx, &queued, from_schedule);
 }
 
 static void __blk_mq_flush_plug_list(struct request_queue *q,
@@ -2655,8 +2633,7 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 				return;
 		}
 
-		blk_mq_run_dispatch_ops(q,
-				blk_mq_plug_issue_direct(plug, false));
+		blk_mq_run_dispatch_ops(q, blk_mq_plug_issue(plug, false));
 		if (rq_list_empty(plug->mq_list))
 			return;
 	}