Re: [syzbot] [kernfs?] possible deadlock in kernfs_fop_llseek

Al Viro
2024-04-06T03:54:57Z

On Fri, Apr 05, 2024 at 08:51:35AM +0200, Christoph Hellwig wrote:
> On Thu, Apr 04, 2024 at 12:33:40PM +0300, Amir Goldstein wrote:
> > I don't follow what you are saying.
> > Which code is in non-starter violation?
> > kernfs for calling lookup_bdev() with internal of->mutex held?
>
> That is a huge problem, and has been causing endless annoying lockdep
> chains in the block layer for us. If we have some way to kill this
> the whole block layer would benefit.

Specifically of->mutex or having pathwalk done from some ->write_iter()?

Incidentally, losetup happily accepts sysfs files as backing store.
I don't think it adds problems we don't have otherwise, but IMO
that's really bogus...