linux-kernel - Re: block: properly handle flush/fua requests in blk_insert_cloned

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Date:	Tue, 9 Aug 2011 15:05:09 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, Jeff Moyer <jmoyer@...hat.com>,
	linux-kernel@...r.kernel.org, Jens Axboe <jaxboe@...ionio.com>,
	dm-devel@...hat.com
Subject: Re: block: properly handle flush/fua requests in
 blk_insert_cloned_request

On Tue, Aug 09, 2011 at 02:55:31PM -0400, Mike Snitzer wrote:

[..]
> > > +	/*
> > > +	 * All FLUSH/FUA requests are expected to have gone through the
> > > +	 * flush machinary.  If a request's cmd_flags doesn't match the
> > > +	 * flush_flags of the underlying request_queue it is a bug.
> > > +	 */
> > > +	BUG_ON((rq->cmd_flags & REQ_FLUSH) && !(q->flush_flags & REQ_FLUSH));
> > > +	BUG_ON((rq->cmd_flags & REQ_FUA) && !(q->flush_flags & REQ_FUA));
> > > +
> > 
> > Actually this makes sense and is simple. :-) Is BUG_ON() too harsh, how
> > about WARN_ONCE() variants? To me system continues to work so warning 
> > is probably good enough.
> 
> Sure, WARN_ONCE() is fine by me.
> 
> Seems Tejun wants a more involved fix though.

Fixing it properly doesn't hurt. Makes it more future proof. In fact I am
thinking what happens to blk_execute_rq() variants where one can prepare a
request and send it down. What if caller sets FLUSH/FUA flags there.

Thanks
Vivek
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