Re: [PATCH] scsi: libsas: Fix dev_list race conditions with proper locking

[Damien Le Moal <dlemoal@kernel.org>]

On 1/31/26 20:19, Chaohai Chen wrote:
>>> +	 * We need to unlock before calling sas_unregister_dev() as it
>>> +	 * may sleep, but we hold a reference to prevent device removal.
>>
>> And why is that necessary ?
>>
> Because when unlocked, it is possible that the device has already been 
> released by another thread. If there is no reference count, it will lead
> to used after free.

Please clearly explain the problem path. Your statements about "another thread"
is too vague.

>>> +	 */
>>> +	spin_lock_irq(&port->dev_list_lock);
>>>  	list_for_each_entry_safe_reverse(dev, n, &port->dev_list, dev_list_node) {
>>>  		if (gone)
>>>  			set_bit(SAS_DEV_GONE, &dev->state);
>>> +		kref_get(&dev->kref);
>>> +		spin_unlock_irq(&port->dev_list_lock);
>>> +
>>>  		sas_unregister_dev(port, dev);
>>> +		sas_put_device(dev);
>>> +
>>> +		spin_lock_irq(&port->dev_list_lock);
>>>  	}
>>> +	spin_unlock_irq(&port->dev_list_lock);

-- 
Damien Le Moal
Western Digital Research