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

From: Tejun Heo
Date: Mon Feb 28 2011 - 10:56:39 EST

On Mon, Feb 28, 2011 at 10:51:45AM -0500, Vivek Goyal wrote:
> o Dominik Klein reported a system hang issue while doing some blkio throttling
> testing.
> 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.
> Cc: stable@xxxxxxxxxx
> Reported-by: Dominik Klein <dk@xxxxxxxxxxxxxxxx>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>

Acked-by: Tejun Heo <tj@xxxxxxxxxx>


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