[PATCH 1/2] sbitmap: add helpers for add/del wait queue handling

[Jens Axboe <axboe@kernel.dk>]

After commit 5d2ee7122c73, users of sbitmap that need wait queue
handling must use the provided helpers. But we only added
prepare_to_wait()/finish_wait() style helpers, add the equivalent
add_wait_queue/list_del wrappers as we..

This is needed to ensure kyber plays by the sbitmap waitqueue
rules.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 include/linux/sbitmap.h | 16 ++++++++++++++--
 lib/sbitmap.c           | 30 ++++++++++++++++++++++++++----
 2 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index 03f50fcedc79..14d558146aea 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -560,13 +560,13 @@ void sbitmap_queue_wake_up(struct sbitmap_queue *sbq);
 void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m);
 
 struct sbq_wait {
-	int accounted;
+	struct sbitmap_queue *sbq;	/* if set, sbq_wait is accounted */
 	struct wait_queue_entry wait;
 };
 
 #define DEFINE_SBQ_WAIT(name)							\
 	struct sbq_wait name = {						\
-		.accounted = 0,							\
+		.sbq = NULL,							\
 		.wait = {							\
 			.private	= current,				\
 			.func		= autoremove_wake_function,		\
@@ -588,4 +588,16 @@ void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq,
 void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws,
 				struct sbq_wait *sbq_wait);
 
+/*
+ * Wrapper around add_wait_queue(), which maintains some extra internal state
+ */
+void sbitmap_add_wait_queue(struct sbitmap_queue *sbq,
+			    struct sbq_wait_state *ws,
+			    struct sbq_wait *sbq_wait);
+
+/*
+ * Must be paired with sbitmap_add_wait_queue()
+ */
+void sbitmap_del_wait_queue(struct sbq_wait *sbq_wait);
+
 #endif /* __LINUX_SCALE_BITMAP_H */
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 5b3e56d68dab..65c2d06250a6 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -671,13 +671,35 @@ void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
 }
 EXPORT_SYMBOL_GPL(sbitmap_queue_show);
 
+void sbitmap_add_wait_queue(struct sbitmap_queue *sbq,
+			    struct sbq_wait_state *ws,
+			    struct sbq_wait *sbq_wait)
+{
+	if (!sbq_wait->sbq) {
+		sbq_wait->sbq = sbq;
+		atomic_inc(&sbq->ws_active);
+	}
+	add_wait_queue(&ws->wait, &sbq_wait->wait);
+}
+EXPORT_SYMBOL_GPL(sbitmap_add_wait_queue);
+
+void sbitmap_del_wait_queue(struct sbq_wait *sbq_wait)
+{
+	list_del_init(&sbq_wait->wait.entry);
+	if (sbq_wait->sbq) {
+		atomic_dec(&sbq_wait->sbq->ws_active);
+		sbq_wait->sbq = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(sbitmap_del_wait_queue);
+
 void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq,
 			     struct sbq_wait_state *ws,
 			     struct sbq_wait *sbq_wait, int state)
 {
-	if (!sbq_wait->accounted) {
+	if (!sbq_wait->sbq) {
 		atomic_inc(&sbq->ws_active);
-		sbq_wait->accounted = 1;
+		sbq_wait->sbq = sbq;
 	}
 	prepare_to_wait_exclusive(&ws->wait, &sbq_wait->wait, state);
 }
@@ -687,9 +709,9 @@ void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws,
 			 struct sbq_wait *sbq_wait)
 {
 	finish_wait(&ws->wait, &sbq_wait->wait);
-	if (sbq_wait->accounted) {
+	if (sbq_wait->sbq) {
 		atomic_dec(&sbq->ws_active);
-		sbq_wait->accounted = 0;
+		sbq_wait->sbq = NULL;
 	}
 }
 EXPORT_SYMBOL_GPL(sbitmap_finish_wait);
-- 
2.17.1