Re: [syzbot] INFO: task hung in vhost_work_dev_flush

[Stefano Garzarella]

On Mon, Feb 21, 2022 at 09:23:04PM +0530, Anirudh Rayabharam wrote:
> On Mon, Feb 21, 2022 at 03:12:33PM +0100, Stefano Garzarella wrote:
> > #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
> > f71077a4d84b
> >
> > Patch sent upstream:
> > https://lore.kernel.org/virtualization/20220221114916.107045-1-sgarzare@xxxxxxxxxx/T/#u
>
> I don't see how your patch fixes this issue. It looks unrelated. It is
> surprising that syzbot is happy with it.
>
> I have sent a patch for this issue here:
> https://lore.kernel.org/lkml/20220221072852.31820-1-mail@xxxxxxxxxxxxx/

It is related because the worker thread is accessing the iotlb that is 
going to be freed, so it could be corrupted/invalid.

Your patch seems right, but simply prevents iotlb from being set for the 
the specific test case, so it remains NULL and iotlb_access_ok() exits 
immediately.

Anyway, currently if nregions is 0 vhost_set_memory() sets an iotlb with 
no regions (the for loop is not executed), so I'm not sure 
iotlb_access_ok() cycles infinitely.

Stefano