linux-kernel - Re: [PATCH 4/6] nouveau: unlock mmap_sem on all errors from nouveau_range

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Message-ID: <20190723173032.GF15357@ziepe.ca>
Date:   Tue, 23 Jul 2019 14:30:32 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Christoph Hellwig <hch@....de>
Cc:     Jérôme Glisse <jglisse@...hat.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] nouveau: unlock mmap_sem on all errors from
 nouveau_range_fault

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.

Jason