Re: [PATCH] block: check bio alignment in blk_mq_submit_bio

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

On Wed, Jun 19, 2024 at 09:50:38AM +0200, Hannes Reinecke wrote:
> On 6/19/24 05:34, Ming Lei wrote:
> > IO logical block size is one fundamental queue limit, and every IO has
> > to be aligned with logical block size because our bio split can't deal
> > with unaligned bio.
> > 
> > The check has to be done with queue usage counter grabbed because device
> > reconfiguration may change logical block size, and we can prevent the
> > reconfiguration from happening by holding queue usage counter.
> > 
> > logical_block_size stays in the 1st cache line of queue_limits, and this
> > cache line is always fetched in fast path via bio_may_exceed_limits(),
> > so IO perf won't be affected by this check.
> > 
> > Cc: Yi Zhang <yi.zhang@redhat.com>
> > Cc: Christoph Hellwig <hch@infradead.org>
> > Cc: Ye Bin <yebin10@huawei.com>
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> >   block/blk-mq.c | 24 ++++++++++++++++++++++++
> >   1 file changed, 24 insertions(+)
> > 
> Is this still an issue after the atomic queue limits patchset from
> Christoph?
> One of the changes there is that we now always freeze the queue before
> changing any limits.
> So really this check should never trigger.

submit_bio() just blocks on queue freezing, and once queue is unfrozen,
submit_bio() still moves on, then unaligned bio is issued to
driver/hardware, please see:

https://lore.kernel.org/linux-block/ZnDmXsFIPmPlT6Si@fedora/T/#m48c098e6d2df142da97ee3992b47d2b7e942a161


Thanks,
Ming