[PATCH 3/4] blk-throtl: introduce blk_throtl_cancel_bios()

[Yu Kuai]

This function is used to cancel all throttled bios when queue is
dying. Noted this modification is mainly from revertion of commit
b77412372b68 ("blk-throttle: remove blk_throtl_drain").

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 block/blk-throttle.c | 39 +++++++++++++++++++++++++++++++++++++++
 block/blk.h          |  2 ++
 2 files changed, 41 insertions(+)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 3892ead7a0b5..4227dcf2dd3b 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -2435,6 +2435,45 @@ static void tg_drain_bios(struct throtl_service_queue *parent_sq)
 	}
 }
 
+/**
+ * blk_throtl_cancel_bios - cancel throttled bios
+ * @q: request_queue to cancel throttled bios for
+ *
+ * This function is called when queue is dying, error all currently
+ * throttled bios on @q so that user threads that are waiting for the bios
+ * can exit.
+ */
+void blk_throtl_cancel_bios(struct request_queue *q)
+{
+	struct throtl_data *td = q->td;
+	struct blkcg_gq *blkg;
+	struct cgroup_subsys_state *pos_css;
+	struct bio *bio;
+	int rw;
+
+	rcu_read_lock();
+
+	/*
+	 * Drain each tg while doing post-order walk on the blkg tree, so
+	 * that all bios are propagated to td->service_queue.  It'd be
+	 * better to walk service_queue tree directly but blkg walk is
+	 * easier.
+	 */
+	blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg)
+		tg_drain_bios(&blkg_to_tg(blkg)->service_queue);
+
+	/* finally, transfer bios from top-level tg's into the td */
+	tg_drain_bios(&td->service_queue);
+
+	rcu_read_unlock();
+
+	/* all bios now should be in td->service_queue, cancel them */
+	for (rw = READ; rw <= WRITE; rw++)
+		while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
+						NULL)))
+			bio_io_error(bio);
+}
+
 int blk_throtl_init(struct request_queue *q)
 {
 	struct throtl_data *td;
diff --git a/block/blk.h b/block/blk.h
index 7d2a0ba7ed21..c407581a3a19 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -287,12 +287,14 @@ int create_task_io_context(struct task_struct *task, gfp_t gfp_mask, int node);
  * Internal throttling interface
  */
 #ifdef CONFIG_BLK_DEV_THROTTLING
+extern void blk_throtl_cancel_bios(struct request_queue *q);
 extern int blk_throtl_init(struct request_queue *q);
 extern void blk_throtl_exit(struct request_queue *q);
 extern void blk_throtl_register_queue(struct request_queue *q);
 extern void blk_throtl_charge_bio_split(struct bio *bio);
 bool blk_throtl_bio(struct bio *bio);
 #else /* CONFIG_BLK_DEV_THROTTLING */
+static inline void blk_throtl_cancel_bios(struct request_queue *q) { }
 static inline int blk_throtl_init(struct request_queue *q) { return 0; }
 static inline void blk_throtl_exit(struct request_queue *q) { }
 static inline void blk_throtl_register_queue(struct request_queue *q) { }
-- 
2.31.1