block: remove BLK_MQ_F_NO_SCHED

The only queues that really can't support a scheduler are those that
do not have a gendisk associated with them, and thus can't be used for
non-passthrough commands.  In addition to those null_blk can optionally
set the flag, which is a bad odd.  Replace the null_blk usage with
BLK_MQ_F_NO_SCHED_BY_DEFAULT to keep the expected semantics and then
remove BLK_MQ_F_NO_SCHED as the non-disk queues never call into
elevator_init_mq or blk_register_queue which adds the sysfs attributes.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250106083531.799976-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-debugfs.c

@@ -185,7 +185,6 @@ static const char *const hctx_flag_name[] = {
 	HCTX_FLAG_NAME(STACKING),
 	HCTX_FLAG_NAME(TAG_HCTX_SHARED),
 	HCTX_FLAG_NAME(BLOCKING),
-	HCTX_FLAG_NAME(NO_SCHED),
 	HCTX_FLAG_NAME(NO_SCHED_BY_DEFAULT),
 };
 #undef HCTX_FLAG_NAME

block/bsg-lib.c

@@ -381,7 +381,7 @@ struct request_queue *bsg_setup_queue(struct device *dev, const char *name,
 	set->queue_depth = 128;
 	set->numa_node = NUMA_NO_NODE;
 	set->cmd_size = sizeof(struct bsg_job) + dd_job_size;
-	set->flags = BLK_MQ_F_NO_SCHED | BLK_MQ_F_BLOCKING;
+	set->flags = BLK_MQ_F_BLOCKING;
 	if (blk_mq_alloc_tag_set(set))
 		goto out_tag_set;
 

block/elevator.c

@@ -547,14 +547,6 @@ void elv_unregister(struct elevator_type *e)
 }
 EXPORT_SYMBOL_GPL(elv_unregister);
 
-static inline bool elv_support_iosched(struct request_queue *q)
-{
-	if (!queue_is_mq(q) ||
-	    (q->tag_set->flags & BLK_MQ_F_NO_SCHED))
-		return false;
-	return true;
-}
-
 /*
  * For single queue devices, default to using mq-deadline. If we have multiple
  * queues or mq-deadline is not available, default to "none".
@@ -580,9 +572,6 @@ void elevator_init_mq(struct request_queue *q)
 	struct elevator_type *e;
 	int err;
 
-	if (!elv_support_iosched(q))
-		return;
-
 	WARN_ON_ONCE(blk_queue_registered(q));
 
 	if (unlikely(q->elevator))
@@ -714,9 +703,6 @@ void elv_iosched_load_module(struct gendisk *disk, const char *buf,
 	struct elevator_type *found;
 	const char *name;
 
-	if (!elv_support_iosched(disk->queue))
-		return;
-
 	strscpy(elevator_name, buf, sizeof(elevator_name));
 	name = strstrip(elevator_name);
 
@@ -734,9 +720,6 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
 	char elevator_name[ELV_NAME_MAX];
 	int ret;
 
-	if (!elv_support_iosched(disk->queue))
-		return count;
-
 	strscpy(elevator_name, buf, sizeof(elevator_name));
 	ret = elevator_change(disk->queue, strstrip(elevator_name));
 	if (!ret)
@@ -751,9 +734,6 @@ ssize_t elv_iosched_show(struct gendisk *disk, char *name)
 	struct elevator_type *cur = NULL, *e;
 	int len = 0;
 
-	if (!elv_support_iosched(q))
-		return sprintf(name, "none\n");
-
 	if (!q->elevator) {
 		len += sprintf(name+len, "[none] ");
 	} else {

drivers/block/null_blk/main.c

@@ -1792,7 +1792,7 @@ static int null_init_global_tag_set(void)
 	tag_set.queue_depth = g_hw_queue_depth;
 	tag_set.numa_node = g_home_node;
 	if (g_no_sched)
-		tag_set.flags |= BLK_MQ_F_NO_SCHED;
+		tag_set.flags |= BLK_MQ_F_NO_SCHED_BY_DEFAULT;
 	if (g_shared_tag_bitmap)
 		tag_set.flags |= BLK_MQ_F_TAG_HCTX_SHARED;
 	if (g_blocking)
@@ -1817,7 +1817,7 @@ static int null_setup_tagset(struct nullb *nullb)
 	nullb->tag_set->queue_depth = nullb->dev->hw_queue_depth;
 	nullb->tag_set->numa_node = nullb->dev->home_node;
 	if (nullb->dev->no_sched)
-		nullb->tag_set->flags |= BLK_MQ_F_NO_SCHED;
+		nullb->tag_set->flags |= BLK_MQ_F_NO_SCHED_BY_DEFAULT;
 	if (nullb->dev->shared_tag_bitmap)
 		nullb->tag_set->flags |= BLK_MQ_F_TAG_HCTX_SHARED;
 	if (nullb->dev->blocking)

drivers/nvme/host/apple.c

@@ -1251,7 +1251,6 @@ static int apple_nvme_alloc_tagsets(struct apple_nvme *anv)
 	anv->admin_tagset.timeout = NVME_ADMIN_TIMEOUT;
 	anv->admin_tagset.numa_node = NUMA_NO_NODE;
 	anv->admin_tagset.cmd_size = sizeof(struct apple_nvme_iod);
-	anv->admin_tagset.flags = BLK_MQ_F_NO_SCHED;
 	anv->admin_tagset.driver_data = &anv->adminq;
 
 	ret = blk_mq_alloc_tag_set(&anv->admin_tagset);

drivers/nvme/host/core.c

@@ -4564,7 +4564,6 @@ int nvme_alloc_admin_tag_set(struct nvme_ctrl *ctrl, struct blk_mq_tag_set *set,
 		/* Reserved for fabric connect and keep alive */
 		set->reserved_tags = 2;
 	set->numa_node = ctrl->numa_node;
-	set->flags = BLK_MQ_F_NO_SCHED;
 	if (ctrl->ops->flags & NVME_F_BLOCKING)
 		set->flags |= BLK_MQ_F_BLOCKING;
 	set->cmd_size = cmd_size;

drivers/ufs/core/ufshcd.c

@@ -10412,7 +10412,6 @@ static int ufshcd_add_scsi_host(struct ufs_hba *hba)
 		.nr_hw_queues	= 1,
 		.queue_depth	= hba->nutmrs,
 		.ops		= &ufshcd_tmf_ops,
-		.flags		= BLK_MQ_F_NO_SCHED,
 	};
 	err = blk_mq_alloc_tag_set(&hba->tmf_tag_set);
 	if (err < 0)

include/linux/blk-mq.h

@@ -676,8 +676,6 @@ enum {
 	BLK_MQ_F_STACKING	= 1 << 2,
 	BLK_MQ_F_TAG_HCTX_SHARED = 1 << 3,
 	BLK_MQ_F_BLOCKING	= 1 << 4,
-	/* Do not allow an I/O scheduler to be configured. */
-	BLK_MQ_F_NO_SCHED	= 1 << 5,
 
 	/*
 	 * Select 'none' during queue registration in case of a single hwq