Re: [PATCH 1/9] block: Stop abusing csd.list for fifo_time

[Frederic Weisbecker]

On Mon, Dec 23, 2013 at 09:39:22PM +0100, Jan Kara wrote:
> Block layer currently abuses rq->csd.list.next for storing fifo_time.
> That is a terrible hack and completely unnecessary as well. Union
> achieves the same space saving in a cleaner way.
> 
> Signed-off-by: Jan Kara <jack@xxxxxxx>

Hi Jan,

Taken as is, the patch is fine and it builds.
But later when I finally get rid of csd->list in a subsequent patch,
rq_fifo_clear() callers break the build.

This is because rq_fifo_clear() initialize the csd->list and I'm not
sure how to fix that leftover because I am not clear about the purpose
of that INIT_LIST_HEAD(): is it to reset fifo time or to prepare for
an IPI to be queued?

All in one it looks buggy because if this is to prepare for the IPI,
it's useless as csd.list is not a list head but just a node. Otherwise if it
is to reset fifo_time it's wrong because INIT_LIST_HEAD doesn't initialize
to 0.

Anyway so I did a braindead fix by removing the whole INIT_LIST_HEAD()
from rq_fifo_clear(), see the patch below. Now to be honest I have no idea
what I'm doing.

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