[PATCH] nvmet: don't change model_number on live subsys

[Chaitanya Kulkarni]

On 2/17/21 23:05, Christoph Hellwig wrote:
>> +	mutex_lock(&subsys->lock);
>> +	list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
>> +		connected = true;
>> +		break;
>> +	}
>> +	mutex_unlock(&subsys->lock);
> This could just use list_empty.  But we'd also need to hold the lock
> over the actual change of the model number to avoid a race window.
>
Since subsys model number actual change occurs later in the
nvmet_subsys_attr_model_store() are you saying something like this we need
instead of having a separate helper ?

diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
index 635a7cb45d0b..c9fd98080b55 100644
--- a/drivers/nvme/target/configfs.c
+++ b/drivers/nvme/target/configfs.c
@@ -1145,6 +1145,7 @@ static ssize_t
nvmet_subsys_attr_model_store(struct config_item *item,
        struct nvmet_subsys_model *new_model;
        char *new_model_number;
        int pos = 0, len;
+       int ret = 0;
 
        len = strcspn(page, "\n");
        if (!len)
@@ -1168,15 +1169,23 @@ static ssize_t
nvmet_subsys_attr_model_store(struct config_item *item,
 
        down_write(&nvmet_config_sem);
        mutex_lock(&subsys->lock);
+       /* make sure this subsys is not connected */
+       if (!list_empty(&subsys->ctrls)) {
+               ret = -EINVAL;
+               goto out_unlock;
+       }
+
        new_model = rcu_replace_pointer(subsys->model, new_model,
                                        mutex_is_locked(&subsys->lock));
+
+out_unlock:
        mutex_unlock(&subsys->lock);
        up_write(&nvmet_config_sem);
 
        kfree_rcu(new_model, rcuhead);
        kfree(new_model_number);
 
-       return count;
+       return ret ? ret : count;
 }
 CONFIGFS_ATTR(nvmet_subsys_, attr_model);