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null_blk: fix mutex initialization and configfs teardown race #1037

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null_blk: fix mutex initialization and configfs teardown race #1037

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fbc2721
null_blk: use DEFINE_MUTEX for the file-scope mutex
Jul 6, 2026
0cbd31b
null_blk: give the file-scope mutex a descriptive name
Jul 6, 2026
596c0a6
null_blk: register configfs subsystem after creating default devices
Jul 6, 2026
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50 changes: 22 additions & 28 deletions drivers/block/null_blk/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -66,7 +66,7 @@ struct nullb_page {
#define NULLB_PAGE_FREE (MAP_SZ - 2)

static LIST_HEAD(nullb_list);
static struct mutex lock;
static DEFINE_MUTEX(nullb_list_lock);
static int null_major;
static DEFINE_IDA(nullb_indexes);
static struct blk_mq_tag_set tag_set;
Expand Down Expand Up @@ -423,9 +423,9 @@ static int nullb_apply_submit_queues(struct nullb_device *dev,
{
int ret;

mutex_lock(&lock);
mutex_lock(&nullb_list_lock);
ret = nullb_update_nr_hw_queues(dev, submit_queues, dev->poll_queues);
mutex_unlock(&lock);
mutex_unlock(&nullb_list_lock);

return ret;
}
Expand All @@ -435,9 +435,9 @@ static int nullb_apply_poll_queues(struct nullb_device *dev,
{
int ret;

mutex_lock(&lock);
mutex_lock(&nullb_list_lock);
ret = nullb_update_nr_hw_queues(dev, dev->submit_queues, poll_queues);
mutex_unlock(&lock);
mutex_unlock(&nullb_list_lock);

return ret;
}
Expand Down Expand Up @@ -493,7 +493,7 @@ static ssize_t nullb_device_power_store(struct config_item *item,
return ret;

ret = count;
mutex_lock(&lock);
mutex_lock(&nullb_list_lock);
if (!dev->power && newp) {
if (test_and_set_bit(NULLB_DEV_FL_UP, &dev->flags))
goto out;
Expand All @@ -516,7 +516,7 @@ static ssize_t nullb_device_power_store(struct config_item *item,
}

out:
mutex_unlock(&lock);
mutex_unlock(&nullb_list_lock);
return ret;
}

Expand Down Expand Up @@ -707,10 +707,10 @@ nullb_group_drop_item(struct config_group *group, struct config_item *item)
struct nullb_device *dev = to_nullb_device(item);

if (test_and_clear_bit(NULLB_DEV_FL_UP, &dev->flags)) {
mutex_lock(&lock);
mutex_lock(&nullb_list_lock);
dev->power = false;
null_del_dev(dev->nullb);
mutex_unlock(&lock);
mutex_unlock(&nullb_list_lock);
}
nullb_del_fault_config(dev);
config_item_put(item);
Expand Down Expand Up @@ -2081,14 +2081,14 @@ static struct nullb *null_find_dev_by_name(const char *name)
{
struct nullb *nullb = NULL, *nb;

mutex_lock(&lock);
mutex_lock(&nullb_list_lock);
list_for_each_entry(nb, &nullb_list, list) {
if (strcmp(nb->disk_name, name) == 0) {
nullb = nb;
break;
}
}
mutex_unlock(&lock);
mutex_unlock(&nullb_list_lock);

return nullb;
}
Expand All @@ -2102,9 +2102,9 @@ static int null_create_dev(void)
if (!dev)
return -ENOMEM;

mutex_lock(&lock);
mutex_lock(&nullb_list_lock);
ret = null_add_dev(dev);
mutex_unlock(&lock);
mutex_unlock(&nullb_list_lock);
if (ret) {
null_free_dev(dev);
return ret;
Expand Down Expand Up @@ -2162,24 +2162,20 @@ static int __init null_init(void)
config_group_init(&nullb_subsys.su_group);
mutex_init(&nullb_subsys.su_mutex);

ret = configfs_register_subsystem(&nullb_subsys);
if (ret)
return ret;

mutex_init(&lock);

null_major = register_blkdev(0, "nullb");
if (null_major < 0) {
ret = null_major;
goto err_conf;
}
if (null_major < 0)
return null_major;

for (i = 0; i < nr_devices; i++) {
ret = null_create_dev();
if (ret)
goto err_dev;
}

ret = configfs_register_subsystem(&nullb_subsys);
if (ret)
goto err_dev;

pr_info("module loaded\n");
return 0;

Expand All @@ -2189,8 +2185,6 @@ static int __init null_init(void)
null_destroy_dev(nullb);
}
unregister_blkdev(null_major, "nullb");
err_conf:
configfs_unregister_subsystem(&nullb_subsys);
return ret;
}

Expand All @@ -2202,17 +2196,17 @@ static void __exit null_exit(void)

unregister_blkdev(null_major, "nullb");

mutex_lock(&lock);
mutex_lock(&nullb_list_lock);
while (!list_empty(&nullb_list)) {
nullb = list_entry(nullb_list.next, struct nullb, list);
null_destroy_dev(nullb);
}
mutex_unlock(&lock);
mutex_unlock(&nullb_list_lock);

if (tag_set.ops)
blk_mq_free_tag_set(&tag_set);

mutex_destroy(&lock);
mutex_destroy(&nullb_list_lock);
}

module_init(null_init);
Expand Down