Re: [syzbot] possible deadlock in loop_add

[Desmond Cheong Zhi Xi]

On 16/7/21 7:00 am, Miquel Raynal wrote:
> Hello,
>
> Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx> wrote on Mon, 12 Jul
> 2021 16:29:16 +0800:
>
> > On 12/7/21 1:27 pm, Christoph Hellwig wrote:
> > > On Sat, Jul 10, 2021 at 09:16:38PM +0800, Hillf Danton wrote:
> > > > To break the lock chain, un/register blkdev without mtd_table_mutex held.
> > >
> > > Yes, Desmond Cheong Zhi Xi sent pretty much the same patch on June 18th
> > > (mtd: break circular locks in register_mtd_blktrans), but it did not get
> > > picked up.
> > >    
> >
> > I believe Miquèl was waiting for -rc1 to apply it.
>
> Indeed, I already applied it but did not advertise yet.

Thanks Miquèl!

> > But taking a closer look, although the fix for the register path is the same, Hillf Danton's proposed patch additionally avoids inverting the lock hierarchy on the unregister path. So I believe this new patch should be more robust.
>
> We can definitely do this in two steps if you want.

Sounds good, I'll prepare a patch with Hillf's suggestion for the 
unregister path.

> Thanks,
> Miquèl