From c45e6a037a536530bd25781ac7c989e52deb2a63 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Mon, 20 Aug 2018 13:22:27 -0600
Subject: [PATCH] blk-wbt: fix has-sleeper queueing check
Git-commit: c45e6a037a536530bd25781ac7c989e52deb2a63
Patch-mainline: v4.19-rc1
References: bsc#1135873

We need to do this inside the loop as well, or we can allow new
IO to supersede previous IO.

Tested-by: Anchal Agarwal <anchalag@amazon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Jan Kara <jack@suse.cz>

---
 block/blk-wbt.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -551,8 +551,10 @@ static void __wbt_wait(struct rq_wb *rwb
 {
 	struct rq_wait *rqw = get_rq_wait(rwb, wb_acct);
 	DECLARE_WAITQUEUE(wait, current);
+	bool has_sleeper;
 
-	if (!wq_has_sleeper(&rqw->wait) &&
+	has_sleeper = wq_has_sleeper(&rqw->wait);
+	if (!has_sleeper &&
 			atomic_inc_below(&rqw->inflight, get_limit(rwb, rw)))
 		return;
 
@@ -528,7 +530,8 @@ static void __wbt_wait(struct rq_wb *rwb
 	do {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 
-		if (atomic_inc_below(&rqw->inflight, get_limit(rwb, rw)))
+		if (!has_sleeper &&
+		    atomic_inc_below(&rqw->inflight, get_limit(rwb, rw)))
 			break;
 
 		if (lock) {
@@ -537,6 +540,7 @@ static void __wbt_wait(struct rq_wb *rwb
 			spin_lock_irq(lock);
 		} else
 			io_schedule();
+		has_sleeper = false;
 	} while (1);
 
 	__set_current_state(TASK_RUNNING);