Re: Current qc_defer implementation may lead to infinite recursion

[Tejun Heo <htejun@gmail.com>]

Elias Oltmanns wrote:
> 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.

Hmmm.... it's supposed not to lock up although it can cause busy wait.
I'll test it tomorrow.

Thanks.

-- 
tejun