block: add `struct elv_change_ctx` for unifying elevator change

Add `struct elv_change_ctx` and prepare for unifying elevator change by
elevator_change(). With this way, any input & output parameter can
be provided & observed in top helper.

This way helps to move kobject add/delete & debugfs register/unregister
out of ->elevator_lock & freezing queue.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250505141805.2751237-16-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/elevator.c b/block/elevator.c
index cb54a3791fe5d0ed22867b35fd0480ff39e17733..6cfac8f77d9f4e1e83aeb16b9d014dbe2fa09b61 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -45,6 +45,12 @@
 #include "blk-wbt.h"
 #include "blk-cgroup.h"
 
+/* Holding context data for changing elevator */
+struct elv_change_ctx {
+       const char *name;
+       bool no_uevent;
+};
+
 static DEFINE_SPINLOCK(elv_list_lock);
 static LIST_HEAD(elv_list);
 
@@ -621,7 +627,7 @@ void elevator_init_mq(struct request_queue *q)
  * If switching fails, we are most likely running out of memory and not able
  * to restore the old io scheduler, so leaving the io scheduler being none.
  */
-static int elevator_switch(struct request_queue *q, const char *name)
+static int elevator_switch(struct request_queue *q, struct elv_change_ctx *ctx)
 {
        struct elevator_type *new_e = NULL;
        int ret = 0;
@@ -629,8 +635,8 @@ static int elevator_switch(struct request_queue *q, const char *name)
        WARN_ON_ONCE(q->mq_freeze_depth == 0);
        lockdep_assert_held(&q->elevator_lock);
 
-       if (strncmp(name, "none", 4)) {
-               new_e = elevator_find_get(name);
+       if (strncmp(ctx->name, "none", 4)) {
+               new_e = elevator_find_get(ctx->name);
                if (!new_e)
                        return -EINVAL;
        }
@@ -646,7 +652,7 @@ static int elevator_switch(struct request_queue *q, const char *name)
                ret = blk_mq_init_sched(q, new_e);
                if (ret)
                        goto out_unfreeze;
-               ret = elv_register_queue(q, true);
+               ret = elv_register_queue(q, !ctx->no_uevent);
                if (ret) {
                        elevator_exit(q);
                        goto out_unfreeze;
@@ -656,7 +662,7 @@ static int elevator_switch(struct request_queue *q, const char *name)
                q->elevator = NULL;
                q->nr_requests = q->tag_set->queue_depth;
        }
-       blk_add_trace_msg(q, "elv switch: %s", name);
+       blk_add_trace_msg(q, "elv switch: %s", ctx->name);
 
 out_unfreeze:
        blk_mq_unquiesce_queue(q);
@@ -674,7 +680,7 @@ out_unfreeze:
 /*
  * Switch this queue to the given IO scheduler.
  */
-static int elevator_change(struct request_queue *q, const char *elevator_name)
+static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
 {
        unsigned int memflags;
        int ret = 0;
@@ -683,9 +689,8 @@ static int elevator_change(struct request_queue *q, const char *elevator_name)
 
        memflags = blk_mq_freeze_queue(q);
        mutex_lock(&q->elevator_lock);
-       if (!(q->elevator && elevator_match(q->elevator->type,
-                               elevator_name)))
-               ret = elevator_switch(q, elevator_name);
+       if (!(q->elevator && elevator_match(q->elevator->type, ctx->name)))
+               ret = elevator_switch(q, ctx);
        mutex_unlock(&q->elevator_lock);
        blk_mq_unfreeze_queue(q, memflags);
        return ret;
@@ -701,15 +706,17 @@ void elv_update_nr_hw_queues(struct request_queue *q)
 
        mutex_lock(&q->elevator_lock);
        if (q->elevator && !blk_queue_dying(q) && !blk_queue_registered(q)) {
-               const char *name = q->elevator->type->elevator_name;
+               struct elv_change_ctx ctx = {
+                       .name = q->elevator->type->elevator_name,
+               };
 
                /* force to reattach elevator after nr_hw_queue is updated */
-               elevator_switch(q, name);
+               elevator_switch(q, &ctx);
        }
        mutex_unlock(&q->elevator_lock);
 }
 
-static void elv_iosched_load_module(char *elevator_name)
+static void elv_iosched_load_module(const char *elevator_name)
 {
        struct elevator_type *found;
 
@@ -725,7 +732,7 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
                          size_t count)
 {
        char elevator_name[ELV_NAME_MAX];
-       char *name;
+       struct elv_change_ctx ctx = {};
        int ret;
        struct request_queue *q = disk->queue;
        struct blk_mq_tag_set *set = q->tag_set;
@@ -740,12 +747,12 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
         * queue is the one for the device storing the module file.
         */
        strscpy(elevator_name, buf, sizeof(elevator_name));
-       name = strstrip(elevator_name);
+       ctx.name = strstrip(elevator_name);
 
-       elv_iosched_load_module(name);
+       elv_iosched_load_module(ctx.name);
 
        down_read(&set->update_nr_hwq_lock);
-       ret = elevator_change(q, name);
+       ret = elevator_change(q, &ctx);
        if (!ret)
                ret = count;
        up_read(&set->update_nr_hwq_lock);