linux-kernel - Re: [PATCH v2 13/26] raid5: use bio

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Message-ID: <20120911192641.GH19739@google.com>
Date:	Tue, 11 Sep 2012 12:26:41 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	NeilBrown <neilb@...e.de>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk, tj@...nel.org
Subject: Re: [PATCH v2 13/26] raid5: use bio_reset()

On Tue, Sep 11, 2012 at 03:03:26PM +1000, NeilBrown wrote:
> On Mon, 10 Sep 2012 17:22:24 -0700 Kent Overstreet <koverstreet@...gle.com>
> wrote:
> 
> > Had to shuffle the code around a bit (where bi_rw and bi_end_io were
> > set), but shouldn't really be anything tricky here
> > 
> > Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
> > CC: Jens Axboe <axboe@...nel.dk>
> > CC: NeilBrown <neilb@...e.de>
> > ---
> >  drivers/md/raid5.c | 28 ++++++++++++++--------------
> >  1 file changed, 14 insertions(+), 14 deletions(-)
> > 
> > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> > index 7c19dbe..ebe43f7 100644
> > --- a/drivers/md/raid5.c
> > +++ b/drivers/md/raid5.c
> > @@ -561,14 +561,6 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
> >  		bi = &sh->dev[i].req;
> >  		rbi = &sh->dev[i].rreq; /* For writing to replacement */
> >  
> > -		bi->bi_rw = rw;
> > -		rbi->bi_rw = rw;
> > -		if (rw & WRITE) {
> > -			bi->bi_end_io = raid5_end_write_request;
> > -			rbi->bi_end_io = raid5_end_write_request;
> > -		} else
> > -			bi->bi_end_io = raid5_end_read_request;
> > -
> >  		rcu_read_lock();
> >  		rrdev = rcu_dereference(conf->disks[i].replacement);
> >  		smp_mb(); /* Ensure that if rrdev is NULL, rdev won't be */
> > @@ -643,7 +635,14 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
> >  
> >  			set_bit(STRIPE_IO_STARTED, &sh->state);
> >  
> > +			bio_reset(bi);
> >  			bi->bi_bdev = rdev->bdev;
> > +			bi->bi_rw = rw;
> > +			bi->bi_end_io = (rw & WRITE)
> > +				? raid5_end_write_request
> > +				: raid5_end_read_request;
> > +			bi->bi_private = sh;
> > +
> >  			pr_debug("%s: for %llu schedule op %ld on disc %d\n",
> >  				__func__, (unsigned long long)sh->sector,
> >  				bi->bi_rw, i);
> > @@ -657,12 +656,9 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
> >  			if (test_bit(R5_ReadNoMerge, &sh->dev[i].flags))
> >  				bi->bi_rw |= REQ_FLUSH;
> >  
> > -			bi->bi_flags = 1 << BIO_UPTODATE;
> > -			bi->bi_idx = 0;
> >  			bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
> >  			bi->bi_io_vec[0].bv_offset = 0;
> >  			bi->bi_size = STRIPE_SIZE;
> > -			bi->bi_next = NULL;
> >  			if (rrdev)
> >  				set_bit(R5_DOUBLE_LOCKED, &sh->dev[i].flags);
> >  			generic_make_request(bi);
> > @@ -674,7 +670,14 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
> >  
> >  			set_bit(STRIPE_IO_STARTED, &sh->state);
> >  
> > +			bio_reset(rbi);
> >  			rbi->bi_bdev = rrdev->bdev;
> > +			rbi->bi_rw = rw;
> > +			rbi->bi_end_io = (rw & WRITE)
> > +				? raid5_end_write_request
> > +				: raid5_end_read_request;
> 
> 'rbi->bi_end_io' can only ever be raid5_end_write_request.  We only get here
> on a write.
> I'd be OK with 
>     BUG_ON(!(rw & WRITE));
> but I don't want the condition in the assignment.

I was thinking to myself that if I was doing a bit more with that code,
I'd factor out all the code in the if (rdev) {} into a separate function
that was called twice there. But, I didn't do that here so you're right
- I'll change it and stick a BUG_ON() there.

> The rest looks quite sane.

Thanks!
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