[PATCH] nvme: fix SRCU protection of nvme_ns_head list

[Sagi Grimberg]

>>>    	sector_t capacity = get_capacity(head->disk);
>>>    	int node;
>>> +	int srcu_idx;
>>>    +	srcu_idx = srcu_read_lock(&head->srcu);
>>>    	list_for_each_entry_rcu(ns, &head->list, siblings) {
>>>    		if (capacity != get_capacity(ns->disk))
>>>    			clear_bit(NVME_NS_READY, &ns->flags);
>>>    	}
>>> +	srcu_read_unlock(&head->srcu, srcu_idx);
>>
>> I don't think you need srcu here, rcu_read_lock/unlock is sufficient.
> 
> So the code obviously does not sleep.  But I wonder if anything speaks
> against mixing SRCU and RCU protection for the same list?

I am not an expert, but the point of (s)rcu_synchronize to fence the
reader critical section isn't it? so if the reader doesn't sleep, the
existing rcu_synchronize should be sufficient.