block: simplify elevator reattachment for updating nr_hw_queues

In blk_mq_update_nr_hw_queues(), nr_hw_queues changes and elevator data
depends on it, and elevator has to be reattached, so call elevator_switch()
to force attachment.

Add elv_update_nr_hw_queues() simply for blk_mq_update_nr_hw_queues() to
reattach elevator, since elevator switch isn't likely when running
blk_mq_update_nr_hw_queues(). This way removes the current switch
none and switch back code.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250505141805.2751237-14-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 84395cc3c01239c94a16d72bbd6e3cd34e301531..2a57b793992bf6a51c843865dbec646a4e55834f 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4987,88 +4987,10 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
        return ret;
 }
 
-/*
- * request_queue and elevator_type pair.
- * It is just used by __blk_mq_update_nr_hw_queues to cache
- * the elevator_type associated with a request_queue.
- */
-struct blk_mq_qe_pair {
-       struct list_head node;
-       struct request_queue *q;
-       struct elevator_type *type;
-};
-
-/*
- * Cache the elevator_type in qe pair list and switch the
- * io scheduler to 'none'
- */
-static bool blk_mq_elv_switch_none(struct list_head *head,
-               struct request_queue *q)
-{
-       struct blk_mq_qe_pair *qe;
-
-       qe = kmalloc(sizeof(*qe), GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY);
-       if (!qe)
-               return false;
-
-       /* Accessing q->elevator needs protection from ->elevator_lock. */
-       mutex_lock(&q->elevator_lock);
-
-       if (!q->elevator) {
-               kfree(qe);
-               goto unlock;
-       }
-
-       INIT_LIST_HEAD(&qe->node);
-       qe->q = q;
-       qe->type = q->elevator->type;
-       /* keep a reference to the elevator module as we'll switch back */
-       __elevator_get(qe->type);
-       list_add(&qe->node, head);
-       elevator_disable(q);
-unlock:
-       mutex_unlock(&q->elevator_lock);
-
-       return true;
-}
-
-static struct blk_mq_qe_pair *blk_lookup_qe_pair(struct list_head *head,
-                                               struct request_queue *q)
-{
-       struct blk_mq_qe_pair *qe;
-
-       list_for_each_entry(qe, head, node)
-               if (qe->q == q)
-                       return qe;
-
-       return NULL;
-}
-
-static void blk_mq_elv_switch_back(struct list_head *head,
-                                 struct request_queue *q)
-{
-       struct blk_mq_qe_pair *qe;
-       struct elevator_type *t;
-
-       qe = blk_lookup_qe_pair(head, q);
-       if (!qe)
-               return;
-       t = qe->type;
-       list_del(&qe->node);
-       kfree(qe);
-
-       mutex_lock(&q->elevator_lock);
-       elevator_switch(q, t->elevator_name);
-       /* drop the reference acquired in blk_mq_elv_switch_none */
-       elevator_put(t);
-       mutex_unlock(&q->elevator_lock);
-}
-
 static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
                                                        int nr_hw_queues)
 {
        struct request_queue *q;
-       LIST_HEAD(head);
        int prev_nr_hw_queues = set->nr_hw_queues;
        unsigned int memflags;
        int i;
@@ -5086,15 +5008,6 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
        list_for_each_entry(q, &set->tag_list, tag_set_list)
                blk_mq_freeze_queue_nomemsave(q);
 
-       /*
-        * Switch IO scheduler to 'none', cleaning up the data associated
-        * with the previous scheduler. We will switch back once we are done
-        * updating the new sw to hw queue mappings.
-        */
-       list_for_each_entry(q, &set->tag_list, tag_set_list)
-               if (!blk_mq_elv_switch_none(&head, q))
-                       goto switch_back;
-
        list_for_each_entry(q, &set->tag_list, tag_set_list) {
                blk_mq_debugfs_unregister_hctxs(q);
                blk_mq_sysfs_unregister_hctxs(q);
@@ -5128,9 +5041,8 @@ reregister:
                blk_mq_debugfs_register_hctxs(q);
        }
 
-switch_back:
        list_for_each_entry(q, &set->tag_list, tag_set_list)
-               blk_mq_elv_switch_back(&head, q);
+               elv_update_nr_hw_queues(q);
 
        list_for_each_entry(q, &set->tag_list, tag_set_list)
                blk_mq_unfreeze_queue_nomemrestore(q);

diff --git a/block/blk.h b/block/blk.h
index 678308c8a78fc60cc80031160159d1e2ce0f1ba4..2e00e2e4cf9d259531c0f124d3778d726b273563 100644 (file)
--- a/block/blk.h
+++ b/block/blk.h
@@ -322,8 +322,7 @@ bool blk_bio_list_merge(struct request_queue *q, struct list_head *list,
 
 bool blk_insert_flush(struct request *rq);
 
-int elevator_switch(struct request_queue *q, const char *name);
-void elevator_disable(struct request_queue *q);
+void elv_update_nr_hw_queues(struct request_queue *q);
 void elevator_exit(struct request_queue *q);
 int elv_register_queue(struct request_queue *q, bool uevent);
 void elv_unregister_queue(struct request_queue *q);

diff --git a/block/elevator.c b/block/elevator.c
index 4e58379c4d880f6c5869f397235cbcbdae8f99fe..cabd7a8bb76c1d015763baf61aa38eef5a181ea8 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -621,7 +621,7 @@ 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.
  */
-int elevator_switch(struct request_queue *q, const char *name)
+static int elevator_switch(struct request_queue *q, const char *name)
 {
        struct elevator_type *new_e = NULL;
        int ret = 0;
@@ -682,6 +682,24 @@ static int elevator_change(struct request_queue *q, const char *elevator_name)
        return elevator_switch(q, elevator_name);
 }
 
+/*
+ * The I/O scheduler depends on the number of hardware queues, this forces a
+ * reattachment when nr_hw_queues changes.
+ */
+void elv_update_nr_hw_queues(struct request_queue *q)
+{
+       WARN_ON_ONCE(q->mq_freeze_depth == 0);
+
+       mutex_lock(&q->elevator_lock);
+       if (q->elevator && !blk_queue_dying(q) && !blk_queue_registered(q)) {
+               const char *name = q->elevator->type->elevator_name;
+
+               /* force to reattach elevator after nr_hw_queue is updated */
+               elevator_switch(q, name);
+       }
+       mutex_unlock(&q->elevator_lock);
+}
+
 static void elv_iosched_load_module(char *elevator_name)
 {
        struct elevator_type *found;