linux-kernel - Re: [PATCH] Re: Bio device too big | kernel BUG at mm/filemap.c:537!

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Message-Id: <20070206174035.eccb4e3b.akpm@linux-foundation.org>
Date:	Tue, 6 Feb 2007 17:40:35 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Neil Brown <neilb@...e.de>
Cc:	"Kai" <epimetreus@...tmail.fm>, stable@...e.de, org@...e.de,
	linux-kernel@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH] Re: Bio device too big | kernel BUG at
 mm/filemap.c:537!

On Wed, 7 Feb 2007 12:30:39 +1100
Neil Brown <neilb@...e.de> wrote:

> On Tuesday February 6, akpm@...ux-foundation.org wrote:
> > On Wed, 7 Feb 2007 10:26:56 +1100
> > Neil Brown <neilb@...e.de> wrote:
> > 
> > > +static int bio_fits_rdev(struct bio *bi)
> > > +{
> > > +	request_queue_t *q = bdev_get_queue(bi->bi_bdev);
> > > +
> > > +	if ((bi->bi_size>>9) > q->max_sectors)
> > > +		return 0;
> > > +	blk_recount_segments(q, bi);
> > > +	if (bi->bi_phys_segments > q->max_phys_segments ||
> > > +	    bi->bi_hw_segments > q->max_hw_segments)
> > > +		return 0;
> > > +
> > > +	if (q->merge_bvec_fn)
> > > +		/* it's too hard to apply the merge_bvec_fn at this stage,
> > > +		 * just just give up
> > > +		 */
> > > +		return 0;
> > > +
> > > +	return 1;
> > > +}
> > 
> > Isn't think going to return 0 rather a lot of the time?
> 
> Why do you say that?

Because I was too lazy to go off and work out who's setting merge_bvec_fn.

> merge_bvec_fn is only set for dm, md, pktcdvd.c so what won't cause a
> zero in real-world cases (it rarely makes sense to put a raid5 on top
> of those things).

OK.   Hopefully it'll stay that way...

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