Re: [PATCH] blk-thrttole: Do not use kblockd workqueue for throtl work

[Jens Axboe <jaxboe@fusionio.com>]

On 2011-02-28 10:51, Vivek Goyal wrote:
> o Dominik Klein reported a system hang issue while doing some blkio throttling
>   testing.
> 
>   https://lkml.org/lkml/2011/2/24/173
> 
> o Some tracing revealed that CFQ was not dispatching any more jobs as queue
>   unplug was not happening. And queue unplug was not happening because unplug
>   work was not being called as there was one throttling work on same cpu
>   which as not finished yet. And throttling work had not finished as it
>   was tyring to dispatch a bio to CFQ but all the request descriptors were
>   consume to it was put to sleep.
> 
> o So basically it is a cyclic dependecny between CFQ unplug work and throtl
>   dispatch work. Tejun suggested that use separate workqueue for such cases..
> 
> o This patch uses a separate workqueue for throttle related work and does not
>   rely on kblockd workqueue anymore.

Not good, that's definitely a bug. I'll queue this up for 2.6.38.

-- 
Jens Axboe