Re: [PATCH 4/4] block: don't hold part0's refcount in IO path

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

On Thu, May 07, 2020 at 07:20:50AM -0700, Christoph Hellwig wrote:
> On Thu, May 07, 2020 at 04:52:39PM +0800, Ming Lei wrote:
> > gendisk can't be gone when there is IO activity, so not hold
> > part0's refcount in IO path.
> > 
> > Cc: Yufen Yu <yuyufen@huawei.com>
> > Cc: Christoph Hellwig <hch@infradead.org>
> > Cc: Hou Tao <houtao1@huawei.com>
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> >  block/blk-core.c | 3 ++-
> >  block/genhd.c    | 1 -
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index 826a8980997d..56cc61354671 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -1343,7 +1343,8 @@ void blk_account_io_done(struct request *req, u64 now)
> >  		part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);
> >  		part_dec_in_flight(req->q, part, rq_data_dir(req));
> >  
> > -		hd_struct_put(part);
> > +		if (part->partno)
> > +			hd_struct_put(part);
> >  		part_stat_unlock();
> 
> Doesn't blk_account_io_merge needs the check as well?

You are right, blk_account_io_merge needs it too.

> 
> Maybe it should go into hd_struct_put and the other helpers to be
> centralized?

I think that is doable.

Thanks,
Ming