Re: [PATCH V2] block: fail unaligned bio from submit_bio_noacct()

[Ming Lei <ming.lei@redhat.com>]

On Sun, Mar 24, 2024 at 04:25:04PM -0700, Christoph Hellwig wrote:
> On Sun, Mar 24, 2024 at 09:37:02PM +0800, Ming Lei wrote:
> > +static bool bio_check_alignment(struct bio *bio, struct request_queue *q)
> > +{
> > +	unsigned int bs = q->limits.logical_block_size;
> > +
> > +	if (bio->bi_iter.bi_size & (bs - 1))
> > +		return false;
> > +
> > +	if (bio->bi_iter.bi_sector & ((bs >> SECTOR_SHIFT) - 1))
> > +		return false;
> > +
> > +	return true;
> > +}
> 
> 
> This should still use bdev_logic_block_size.  And maybe it's just me,
> but I think dropping thelines after the false returns would actually
> make it more readle.

OK, will remove the blank line.

> 
> > diff --git a/block/fops.c b/block/fops.c
> > index 679d9b752fe8..75595c728190 100644
> > --- a/block/fops.c
> > +++ b/block/fops.c
> > @@ -37,8 +37,7 @@ static blk_opf_t dio_bio_write_op(struct kiocb *iocb)
> >  static bool blkdev_dio_unaligned(struct block_device *bdev, loff_t pos,
> >  			      struct iov_iter *iter)
> >  {
> > -	return pos & (bdev_logical_block_size(bdev) - 1) ||
> > -		!bdev_iter_is_aligned(bdev, iter);
> > +	return !bdev_iter_is_aligned(bdev, iter);
> 
> If you drop this:
> 
>  - we now actually go all the way down to building and submiting a
>    bio for a trivial bounds check.
>  - your get a trivial to trigger WARN_ON.
> 
> I'd strongly advise against dropping this check.

OK.

Also only q->limits.logical_block_size is fetched for small BS IO
fast path, I think log(lbs) can be cached in request_queue for avoiding the
extra fetch of q.limits. Especially, it could be easier to do so
with your recent queue limit atomic update changes.


Thanks, 
Ming