From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 4 Jun 2020 11:23:39 -0600
Subject: [PATCH] block: provide plug based way of signaling forced no-wait
 semantics
References: bsc#1175995,jsc#SLE-15608
Git-commit: 5a473e8311b582a40c10409a0f4bb39f42aa8123
Patch-mainline: v5.9-rc1

Provide a way for the caller to specify that IO should be marked
with REQ_NOWAIT to avoid blocking on allocation.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 block/blk-core.c       | 6 ++++++
 include/linux/blkdev.h | 1 +
 2 files changed, 7 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index a63df58b745d..af272be686c1 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -917,9 +917,14 @@ generic_make_request_checks(struct bio *bio)
 {
 	struct request_queue *q = bio->bi_disk->queue;
 	blk_status_t status = BLK_STS_IOERR;
+	struct blk_plug *plug;
 
 	might_sleep();
 
+	plug = blk_mq_plug(q, bio);
+	if (plug && plug->nowait)
+		bio->bi_opf |= REQ_NOWAIT;
+
 	/*
 	 * For a REQ_NOWAIT based request, return -EOPNOTSUPP
 	 * if queue is not a request based queue.
@@ -1765,6 +1770,7 @@ void blk_start_plug(struct blk_plug *plug)
 	INIT_LIST_HEAD(&plug->cb_list);
 	plug->rq_count = 0;
 	plug->multiple_queues = false;
+	plug->nowait = false;
 
 	/*
 	 * Store ordering should not be needed here, since a potential
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f226df151f67..f0d08cf01360 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1189,6 +1189,7 @@ struct blk_plug {
 	struct list_head cb_list; /* md requires an unplug callback */
 	unsigned short rq_count;
 	bool multiple_queues;
+	bool nowait;
 };
 #define BLK_MAX_REQUEST_COUNT 16
 #define BLK_PLUG_FLUSH_SIZE (128 * 1024)
-- 
2.16.4