block: split .sysfs_lock into two locks

[linux.git] / block / elevator.c

diff --git a/block/elevator.c b/block/elevator.c
index 03d9231965691a56e6aabb31ca6d27687c158ef8..4781c4205a5d4ba19deb5a1ac2755711748d14ab 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -470,13 +470,16 @@ static struct kobj_type elv_ktype = {
        .release        = elevator_release,
 };
 
-int elv_register_queue(struct request_queue *q)
+/*
+ * elv_register_queue is called from either blk_register_queue or
+ * elevator_switch, elevator switch is prevented from being happen
+ * in the two paths, so it is safe to not hold q->sysfs_lock.
+ */
+int elv_register_queue(struct request_queue *q, bool uevent)
 {
        struct elevator_queue *e = q->elevator;
        int error;
 
-       lockdep_assert_held(&q->sysfs_lock);
-
        error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
        if (!error) {
                struct elv_fs_entry *attr = e->type->elevator_attrs;
@@ -487,24 +490,34 @@ int elv_register_queue(struct request_queue *q)
                                attr++;
                        }
                }
-               kobject_uevent(&e->kobj, KOBJ_ADD);
+               if (uevent)
+                       kobject_uevent(&e->kobj, KOBJ_ADD);
+
+               mutex_lock(&q->sysfs_lock);
                e->registered = 1;
+               mutex_unlock(&q->sysfs_lock);
        }
        return error;
 }
 
+/*
+ * elv_unregister_queue is called from either blk_unregister_queue or
+ * elevator_switch, elevator switch is prevented from being happen
+ * in the two paths, so it is safe to not hold q->sysfs_lock.
+ */
 void elv_unregister_queue(struct request_queue *q)
 {
-       lockdep_assert_held(&q->sysfs_lock);
-
        if (q) {
                struct elevator_queue *e = q->elevator;
 
                kobject_uevent(&e->kobj, KOBJ_REMOVE);
                kobject_del(&e->kobj);
+
+               mutex_lock(&q->sysfs_lock);
                e->registered = 0;
                /* Re-enable throttling in case elevator disabled it */
                wbt_enable_default(q);
+               mutex_unlock(&q->sysfs_lock);
        }
 }
 
@@ -567,10 +580,32 @@ int elevator_switch_mq(struct request_queue *q,
        lockdep_assert_held(&q->sysfs_lock);
 
        if (q->elevator) {
-               if (q->elevator->registered)
+               if (q->elevator->registered) {
+                       mutex_unlock(&q->sysfs_lock);
+
+                       /*
+                        * Concurrent elevator switch can't happen becasue
+                        * sysfs write is always exclusively on same file.
+                        *
+                        * Also the elevator queue won't be freed after
+                        * sysfs_lock is released becasue kobject_del() in
+                        * blk_unregister_queue() waits for completion of
+                        * .store & .show on its attributes.
+                        */
                        elv_unregister_queue(q);
+
+                       mutex_lock(&q->sysfs_lock);
+               }
                ioc_clear_queue(q);
                elevator_exit(q, q->elevator);
+
+               /*
+                * sysfs_lock may be dropped, so re-check if queue is
+                * unregistered. If yes, don't switch to new elevator
+                * any more
+                */
+               if (!blk_queue_registered(q))
+                       return 0;
        }
 
        ret = blk_mq_init_sched(q, new_e);
@@ -578,7 +613,11 @@ int elevator_switch_mq(struct request_queue *q,
                goto out;
 
        if (new_e) {
-               ret = elv_register_queue(q);
+               mutex_unlock(&q->sysfs_lock);
+
+               ret = elv_register_queue(q, true);
+
+               mutex_lock(&q->sysfs_lock);
                if (ret) {
                        elevator_exit(q, q->elevator);
                        goto out;