Re: [PATCH v2 0/3] blk-cgroup: some cleanup

[Bart Van Assche]

On 4/10/23 11:47, Bart Van Assche wrote:
> On 4/9/23 18:57, Yu Kuai wrote:
> > Hi, Bart
> >
> > 在 2023/04/08 2:41, Bart Van Assche 写道:
> > > On 4/6/23 07:50, Chengming Zhou wrote:
> > > > These are some cleanup patches of blk-cgroup. Thanks for review.
> > >
> > > With these patches applied, my kernel test VM crashes during boot. 
> > > The following crash disappears if I revert these patches:
> > >
> > > BUG: KASAN: null-ptr-deref in bio_associate_blkg_from_css+0x83/0x240
> > > Read of size 8 at addr 0000000000000518 by task blkid/5885
> > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 
> > > 1.16.0-debian-1.16.0-5 04/01/2014
> > > Call Trace:
> > >   dump_stack_lvl+0x4a/0x80
> > >   print_report+0x21e/0x260
> > >   kasan_report+0xc2/0xf0
> > >   __asan_load8+0x69/0x90
> > >   bio_associate_blkg_from_css+0x83/0x240
> > >   bfq_bio_bfqg+0xce/0x120 [bfq]
> > >   bfq_bic_update_cgroup+0x2f/0x3c0 [bfq]
> > >   bfq_init_rq+0x1e8/0xb10 [bfq]
> > >   bfq_insert_request.isra.0+0xa3/0x420 [bfq]
> > >   bfq_insert_requests+0xca/0xf0 [bfq]
> > >   blk_mq_dispatch_rq_list+0x4c0/0xb00
> >
> > I found this call trace quite weird, I can't figure out how
> > bfq_insert_requests can be called from blk_mq_dispatch_rq_list,
> > can you show the add2line result?
>
> Hi Kuai,
>
> Thanks for having taken a look. I ran my tests with this patch series on 
> top of Jens' for-next branch: "[PATCH v2 00/12] Submit zoned writes in 
> order" 
> (https://lore.kernel.org/linux-block/20230407235822.1672286-1-bvanassche@xxxxxxx/T/#m4c8c7ca5a5627510dc1709847b11589e8791b6b6). I will take a closer look and see which of these two patch series needs to be adjusted.

(replying to my own e-mail)

I think I found the root cause: bio->bi_bdev is NULL for pass-through 
requests and BFQ doesn't like it that bio->bi_bdev is NULL. I will make 
sure that pass-through requests are not submitted to any I/O scheduler.

Thanks,

Bart.