[PATCH RFC v2 4/6] blk-cgroup: add a new helper blkg_conf_exit_blkg()

[Yu Kuai]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

The new helper just release the spin_lock 'queue_lock' and keep the
mutex 'rq_qos_mutex' held, to allow blk_throttle and other cgroup
policies to be destroyed when they are disabled by user.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 block/blk-cgroup.c | 17 +++++++++++++++++
 block/blk-cgroup.h |  1 +
 2 files changed, 18 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index b5e626a16758..ada9258f78bc 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -949,6 +949,23 @@ void blkg_conf_exit(struct blkg_conf_ctx *ctx)
 }
 EXPORT_SYMBOL_GPL(blkg_conf_exit);
 
+/*
+ * blkg_conf_exit_blkg - like blkg_conf_exit() but only release queue_lock.
+ * @ctx: blkg_conf_ctx initialized with blkg_conf_init()
+ *
+ * This function must be called on all blkg_conf_ctx's initialized with
+ * blkg_conf_init().
+ */
+void blkg_conf_exit_blkg(struct blkg_conf_ctx *ctx)
+	__releases(&ctx->bdev->bd_queue->queue_lock)
+{
+	if (ctx->blkg) {
+		spin_unlock_irq(&bdev_get_queue(ctx->bdev)->queue_lock);
+		ctx->blkg = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(blkg_conf_exit_blkg);
+
 static void blkg_iostat_set(struct blkg_iostat *dst, struct blkg_iostat *src)
 {
 	int i;
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 78b74106bf10..009f96191e71 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -219,6 +219,7 @@ int blkg_conf_open_bdev(struct blkg_conf_ctx *ctx);
 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 		   struct blkg_conf_ctx *ctx);
 void blkg_conf_exit(struct blkg_conf_ctx *ctx);
+void blkg_conf_exit_blkg(struct blkg_conf_ctx *ctx);
 
 /**
  * bio_issue_as_root_blkg - see if this bio needs to be issued as root blkg
-- 
2.39.2