Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 30 Nov 2018 11:17:51 +1100
From:   Sam Bobroff <sbobroff@linux.ibm.com>
To:     Daniel Vetter <daniel@ffwll.ch>
Cc:     "airlied@gmail.com" <airlied@gmail.com>,
        Dave Airlie <airlied@linux.ie>,
        Dave Airlie <airlied@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH 2/2] drm/ast: Fix connector leak during driver unload
References: <cover.1541397462.git.sbobroff@linux.ibm.com>
 <3350c5dd5ea08c71e4769ea3801290e7f9238a6c.1541397462.git.sbobroff@linux.ibm.com>
 <CAPM=9txRjd6E3DxdcM14mzWG1P-Cr70P61Eyce95bBhJtqfH7A@mail.gmail.com>
 <20181129020034.GA10328@tungsten.ozlabs.ibm.com>
 <CAKMK7uEY8C_9qwuUi5rR1+_xYOSXeKicopR1zTpQKaMEJTM-fA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
        protocol="application/pgp-signature"; boundary="YZ5djTAD1cGYuMQK"
Content-Disposition: inline
In-Reply-To: <CAKMK7uEY8C_9qwuUi5rR1+_xYOSXeKicopR1zTpQKaMEJTM-fA@mail.gmail.com>
User-Agent: Mutt/1.9.3 (2018-01-21)
Message-Id: <20181130001750.GA6776@tungsten.ozlabs.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


--YZ5djTAD1cGYuMQK
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Thu, Nov 29, 2018 at 09:56:53AM +0100, Daniel Vetter wrote:
> On Thu, Nov 29, 2018 at 9:05 AM Sam Bobroff <sbobroff@linux.ibm.com> wrot=
e:
> >
> > On Thu, Nov 29, 2018 at 09:40:53AM +1000, Dave Airlie wrote:
> > > On Mon, 5 Nov 2018 at 15:59, Sam Bobroff <sbobroff@linux.ibm.com> wro=
te:
> > > >
> > > > When unloading the ast driver, a warning message is printed by
> > > > drm_mode_config_cleanup() because a reference is still held to one =
of
> > > > the drm_connector structs.
> > > >
> > > > Correct this by calling drm_framebuffer_remove() in
> > > > ast_fbdev_destroy().
> > > >
> > > > Signed-off-by: Sam Bobroff <sbobroff@linux.ibm.com>
> > > > ---
> > > >  drivers/gpu/drm/ast/ast_fb.c | 4 ++++
> > > >  1 file changed, 4 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/ast/ast_fb.c b/drivers/gpu/drm/ast/ast=
_fb.c
> > > > index 0cd827e11fa2..655372ea81e9 100644
> > > > --- a/drivers/gpu/drm/ast/ast_fb.c
> > > > +++ b/drivers/gpu/drm/ast/ast_fb.c
> > > > @@ -263,6 +263,10 @@ static void ast_fbdev_destroy(struct drm_devic=
e *dev,
> > > >  {
> > > >         struct ast_framebuffer *afb =3D &afbdev->afb;
> > > >
> > > > +       /* drm_framebuffer_remove() expects us to hold a ref, which=
 it
> > > > +        * will drop, so take one: */
> > > > +       drm_framebuffer_get(&afb->base);
> > > > +       drm_framebuffer_remove(&afb->base);
> > >
> > > This doesn't seem corret, no other driver does this pattern, and I
> > > can't believe ast is special here.
> > >
> > > The get just doesn't make sense.
> >
> > Thanks for having a look at this, as I said in the cover letter I was
> > concerned that it might not be a good fix.
> >
> > But the AST driver does seem to be special (or just old?) because it
> > embeds the drm_framebuffer directly into ast_fbdev and (almost all)
> > other drivers dynamically allocate and reference count theirs.
> >
> > The drm_framebuffer_get() certainly looks weird but it is there in order
> > to cause drm_framebuffer_remove() to call legacy_remove_fb(), which it
> > won't do unless the refcount is at least 2. (And because the
> > drm_framebuffer isn't dynamically allocated in this case we don't really
> > care about the reference count anyway.)
> >
> > An alternative might be to call legacy_remove_fb() directly, but it's
> > declared static.  Do you think it would be better to expose it and call
> > it directly from the AST driver code? Or is there some other better way
> > to put the drm_connectors?
>=20
> Your problem isn't the dynamic fb vs. embedded fb for fbdev (you're
> already using drm_framebuffer_unregister_private to handle that). Your
> problem is you're not shutting down stuff on driver unload, which
> means the fb is still in use. drm_atomic_helper_shutdown() takes care
> of that for atomic drivers.
>=20
> No idea anymore what to do for legacy code, probably need to open code
> a shutdown sequence. Definitely not the above.
> -Daniel

Well, it looks like drm_crtc_force_disable_all() would also do the job,
and from looking at nouveau_display_fini() it's used there as an
alternative to drm_atomic_helper_shutdown().

Would it be reasonable to call that at the start of
ast_fbdev_destroy() instead? (Testing shows that it does allow the
drm_connector to be released. Is it enough/correct though?)

Cheers,
Sam.

> --=20
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>=20

--YZ5djTAD1cGYuMQK
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iQEzBAABCAAdFiEELWWF8pdtWK5YQRohMX8w6AQl/iIFAlwAgaIACgkQMX8w6AQl
/iK4kwf/VNV58jJRgG00g3xQieQoDUoOUx0p72lWp4ucR+wbvou7paqyPMDwUPhG
CY8Lg9D+X1cAKP4uCmotGBHeKMSTDy3pEgjbIC4BxcN2dDxKdyON29u8CnqDnF40
6S2TGyMIV2I4VdejyuFmPAPoSqJG5p28zLBzsAxoIh0Va8lSjrXOejz0x/OU3Tt4
FM0W/SDiNTIBARDvPBgWiCuWpCPECid4/oNlheyCF2+t6jTCaJLaZ03X7f35y8AL
qjT9gh7GeVC3Sip1GXiFVWVT63WlDpf72LMuT5qMZrQtLOXSXZxuiKYGbAO8qijE
aEiv7WfgOI4ufoiv4reFIAPKvaQ1iA==
=su7o
-----END PGP SIGNATURE-----

--YZ5djTAD1cGYuMQK--