Re: [syzbot] possible deadlock in loop_add

[Miquel Raynal]

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.

> 
> 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.

Thanks,
Miquèl