linux-kernel - Re: [GIT PULL] two more s390 bug fixes for 4.17

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Date:   Wed, 30 May 2018 11:11:40 +0200
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [GIT PULL] two more s390 bug fixes for 4.17

On Wed, 30 May 2018 00:41:30 -0700
Christoph Hellwig <hch@...radead.org> wrote:

> > -	req->completion_data = cqr;
> > +	*((struct dasd_ccw_req **) blk_mq_rq_to_pdu(req)) = cqr;
> > +  
> 
> Please don't play such tricks.  In general your driver structure
> should have struct request embedded.  If for some reason
> struct dasd_ccw_req has a different life time please create a new
> structure instead of these hacks.

Why do you consider this to be a 'trick'? The blk_mq_rq_to_pdu is
meant to be used to access a block of data that is is associated
with a request, no? With the change we store a single value, the
pointer to a struct dasd_ccw_req. The struct request comes first,
later do_dasd_request creates the struct dasd_ccw_req with the
CCW chain for the request. And for the blk timeout handler we need
a way to find the dasd_ccw_req again.

> In either way this really doesn't look like a post-rc7 change.

You think so? It fixes a crash for s390 with a minimal number of
changed lines:

 drivers/s390/block/dasd.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.