Re: [OOPS, 3.13-rc2] null ptr in dio_complete()

[Dave Chinner <david@fromorbit.com>]

On Fri, Dec 06, 2013 at 08:26:51AM +1100, Dave Chinner wrote:
> On Thu, Dec 05, 2013 at 10:22:20PM +0800, Ming Lei wrote:
> > On Wed, 4 Dec 2013 12:58:38 +1100
> > Dave Chinner <david@fromorbit.com> wrote:
> > 
> > > 
> > > And I just hit this from running xfs_repair which is doing
> > > multithreaded direct IO directly on /dev/vdc:
> .....
> > > So this is looking like another virtio+blk_mq problem....
> > 
> > This one might be caused by using-after-'free' request because the freed
> > request may be allocated to another CPU immediately, and the below patch
> > may be helpful, would you mind testing it?
> > 
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 6875736..2358bdf 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -311,12 +311,12 @@ void blk_mq_complete_request(struct request *rq, int error)
> >  
> >  	blk_account_io_completion(rq, bytes);
> >  
> > +	blk_account_io_done(rq);
> > +
> >  	if (rq->end_io)
> >  		rq->end_io(rq, error);
> >  	else
> >  		blk_mq_free_request(rq);
> > -
> > -	blk_account_io_done(rq);
> >  }
> >  
> >  void __blk_mq_end_io(struct request *rq, int error)
> 
> Testing it now. I'll let you know how it goes in couple of hours.

Ok, this looks like it is working correctly. The read/write io stats
are now working properly, too. Thanks for finding the problem
quickly!

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com