Re: [PATCH 4/6] nouveau: unlock mmap_sem on all errors from nouveau_range_fault

From: Jason Gunthorpe
Date: Tue Jul 23 2019 - 13:30:36 EST

On Tue, Jul 23, 2019 at 07:23:35PM +0200, Christoph Hellwig wrote:
> On Tue, Jul 23, 2019 at 02:17:31PM -0300, Jason Gunthorpe wrote:
> > That reminds me, this code is also leaking hmm_range_unregister() in
> > the success path, right?
> No, that is done by hmm_vma_range_done / nouveau_range_done for the
> success path.

.. which is done with the mmap_sem held :(

> > I think the right way to structure this is to move the goto again and
> > related into the nouveau_range_fault() so the whole retry algorithm is
> > sensibly self contained.
> Then we'd take svmm->mutex inside the helper and let the caller
> unlock that. Either way it is a bit of a mess, and I'd rather prefer
> if someone has the hardware would do a grand rewrite of this path
> eventually. Alternatively if no one signs up to mainain this code
> we should eventually drop it given the staging status.

I tend to agree with the sentiment, it just makes me sad that all the
examples we have of these APIs are so troubled.