[SRU B][PATCH v2 3/7] blk-wbt: move disable check into get_limit()

[Mauricio Faria de Oliveira]

From: Jens Axboe <axboe at kernel.dk>

BugLink: https://bugs.launchpad.net/bugs/1810998

Check it in one place, instead of in multiple places.

Tested-by: Anchal Agarwal <anchalag at amazon.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
(backported from commit ffa358dcaae1f2f00926484e712e06daa8953cb4)
[mfo: backport:
 - blk-wbt.c:
   - hunk 1: refresh lower context lines due to lack of commit
     782f569774d7 ("blk-wbt: throttle discards like background
     writes"), not required / introduces a new thing/behavior.]
   - hunk 2: s/rq_wait_inc_below(rqw/atomic_inc_below(&rqw->inflight/
   - hunk 3: s/rq_wait_inc_below(rqw/atomic_inc_below(&rqw->inflight/
Signed-off-by: Mauricio Faria de Oliveira <mfo at canonical.com>
---
 block/blk-wbt.c | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 145f192a8007..0d3c01cfe30c 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -483,6 +483,13 @@ static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw)
 {
 	unsigned int limit;
 
+	/*
+	 * If we got disabled, just return UINT_MAX. This ensures that
+	 * we'll properly inc a new IO, and dec+wakeup at the end.
+	 */
+	if (!rwb_enabled(rwb))
+		return UINT_MAX;
+
 	/*
 	 * At this point we know it's a buffered write. If this is
 	 * kswapd trying to free memory, or REQ_SYNC is set, then
@@ -517,16 +524,6 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
 	struct rq_wait *rqw = get_rq_wait(rwb, wb_acct);
 	DECLARE_WAITQUEUE(wait, current);
 
-	/*
-	* inc it here even if disabled, since we'll dec it at completion.
-	* this only happens if the task was sleeping in __wbt_wait(),
-	* and someone turned it off at the same time.
-	*/
-	if (!rwb_enabled(rwb)) {
-		atomic_inc(&rqw->inflight);
-		return;
-	}
-
 	if (!waitqueue_active(&rqw->wait)
 		&& atomic_inc_below(&rqw->inflight, get_limit(rwb, rw)))
 		return;
@@ -535,11 +532,6 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
 	do {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 
-		if (!rwb_enabled(rwb)) {
-			atomic_inc(&rqw->inflight);
-			break;
-		}
-
 		if (atomic_inc_below(&rqw->inflight, get_limit(rwb, rw)))
 			break;
 
-- 
2.17.1