block: move q->sysfs_lock and queue-freeze under show/store method

In preparation to further simplify and group sysfs attributes which
don't require locking or require some form of locking other than q->
limits_lock, move acquire/release of q->sysfs_lock and queue freeze/
unfreeze under each attributes' respective show/store method.

While we are at it, also remove ->load_module() as it's used to load
the module before queue is freezed. Now as we moved queue-freeze under
->store(), we could load module directly from the attributes' store
method before we actually start freezing the queue. Currently, the
->load_module() is only used by "scheduler" attribute, so we now load
the relevant elevator module before we start freezing the queue in
elv_iosched_store().

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250304102551.2533767-3-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 18 insertions, 2 deletions

diff --git a/block/elevator.c b/block/elevator.c
index cd2ce4921601..041f1d983bc7 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -723,11 +723,24 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
 {
 	char elevator_name[ELV_NAME_MAX];
 	int ret;
+	unsigned int memflags;
+	struct request_queue *q = disk->queue;
 
+	/*
+	 * If the attribute needs to load a module, do it before freezing the
+	 * queue to ensure that the module file can be read when the request
+	 * queue is the one for the device storing the module file.
+	 */
+	elv_iosched_load_module(disk, buf, count);
 	strscpy(elevator_name, buf, sizeof(elevator_name));
-	ret = elevator_change(disk->queue, strstrip(elevator_name));
+
+	mutex_lock(&q->sysfs_lock);
+	memflags = blk_mq_freeze_queue(q);
+	ret = elevator_change(q, strstrip(elevator_name));
 	if (!ret)
-		return count;
+		ret = count;
+	blk_mq_unfreeze_queue(q, memflags);
+	mutex_unlock(&q->sysfs_lock);
 	return ret;
 }
 
@@ -738,6 +751,7 @@ ssize_t elv_iosched_show(struct gendisk *disk, char *name)
 	struct elevator_type *cur = NULL, *e;
 	int len = 0;
 
+	mutex_lock(&q->sysfs_lock);
 	if (!q->elevator) {
 		len += sprintf(name+len, "[none] ");
 	} else {
@@ -755,6 +769,8 @@ ssize_t elv_iosched_show(struct gendisk *disk, char *name)
 	spin_unlock(&elv_list_lock);
 
 	len += sprintf(name+len, "\n");
+	mutex_unlock(&q->sysfs_lock);
+
 	return len;
 }