Re: INFO: task hung in blk_queue_enter

[Jens Axboe]

On 6/1/18 8:36 PM, Ming Lei wrote:
>> clear the bit when we need to, potentially even adding a debug check to
>> blk_queue_enter_live() that complains if the ref was not already
>> elevated. Though that would be expensive, compared to the percpu inc
>> now. Not saying the bit is necessarily the best way forward, but I do
>> like it a LOT more than adding an argument to generic_make_request.
> 
> We may introduce generic_make_request_with_ref() for blk_queue_split(),
> what do you think of the following patch?

Functionally it'll work as well.

> In DM or MD, there is the following use case:
> 
> 1) bio comes from fs, then one clone is made from this bio
> 
> 2) the cloned bio is submitted via generic_make_request() from
> another context, such as wq.
> 
> 3) then the flag of BIO_QUEUE_ENTERED is inherited and causes
> the queue usage counter isn't held.

We don't copy flags on a clone.

-- 
Jens Axboe