Re: [PATCH v3] nullb: Prevent use of legacy request queue mode

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2019/02/12 11:55, Jens Axboe wrote:
> On 2/11/19 4:47 PM, Damien Le Moal wrote:
>> When null_blk queue mode is specified together with modprobe/insmod, a
>> check to prevent setting the nullb device queue mode to 1 (NULL_Q_RQ) is
>> done. However, the same check is not performed when setting up a nullb
>> device through configfs, resulting in a oops (NULL pointer dereference
>> for the device request queue).
>>
>> Fix this problem by checking for an invalid queue mode value in
>> null_validate_conf(), propagating -EINVAL to null_add_dev() if the queue
>> mode is NULL_Q_RQ. While at it, also fix the propagation to user space
>> of null_add_dev() return value when a nullb device is created through
>> the power attribute of configfs.
>>
>> Finally, remove the "1=rq" value from the list of possible values of
>> the queue_mode module argument to make it clear that this is no longer
>> a valid setting.
> 
> I actually left that in there on purpose, to avoid breaking test
> scripts. It's not the perfect solution, but I viewed it as the
> lesser of two evils. Maybe we're fine now, I think blktests has
> been fixed a while back?
> 

Yes, blktests is fine right now and not triggering the problem with a default
config. Internally, blktests never tries to enable the rq=1 mode. I discovered
this problem doing tests manually.

-- 
Damien Le Moal
Western Digital Research