Re: Current qc_defer implementation may lead to infinite recursion

[Elias Oltmanns <eo@nebensachen.de>]

Tejun Heo <htejun@gmail.com> wrote:
> Elias Oltmanns wrote:
>> This proves that piix_qc_defer() has declined the same command 100
>> times in succession. However, this will only happen if the status of
>> all the commands enqueued for one port hasn't changed in the
>> meantime. This suggests to me that the threads scheduled for command
>> execution and completion aren't served for some reason. Any ideas?
>
> Blocked counts of 1 will cause busy looping because when blk_run_queue()
> returns because it's recursing too deep, it schedules unplug work right
> away, so it will easily loop 100 times.  Max blocked counts should be
> adjusted to two (needs some testing before actually submitting the
> change).  But that still shouldn't cause any lock up.  What happens if
> you remove the 100 times limit?  Does the machine hang on IO?

Yes, it does. In fact, I had already verified that before sending the
previous email.

Regards,

Elias