RE: [PATCH 1/3] drm: Restore driver.preclose() for all to use

From: "Tang, CQ" <cq.tang@intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	Daniel Vetter <daniel@ffwll.ch>,
	 Dave Airlie <airlied@redhat.com>
Cc: Gustavo Padovan <gustavo.padovan@collabora.com>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	stable <stable@vger.kernel.org>,
	"Vetter, Daniel" <daniel.vetter@intel.com>
Subject: RE: [PATCH 1/3] drm: Restore driver.preclose() for all to use
Date: Wed, 29 Jul 2020 15:09:42 +0000	[thread overview]
Message-ID: <0118a278832d4dde8d8d71e3db635869@intel.com> (raw)
In-Reply-To: <159595365380.28639.1774414370144556112@build.alporthouse.com>

> -----Original Message-----
> From: Chris Wilson <chris@chris-wilson.co.uk>
> Sent: Tuesday, July 28, 2020 9:28 AM
> To: Daniel Vetter <daniel@ffwll.ch>; Dave Airlie <airlied@redhat.com>
> Cc: intel-gfx <intel-gfx@lists.freedesktop.org>; stable
> <stable@vger.kernel.org>; Gustavo Padovan
> <gustavo.padovan@collabora.com>; Tang, CQ <cq.tang@intel.com>; dri-
> devel <dri-devel@lists.freedesktop.org>; Vetter, Daniel
> <daniel.vetter@intel.com>
> Subject: Re: [PATCH 1/3] drm: Restore driver.preclose() for all to use
> 
> Quoting Daniel Vetter (2020-07-27 20:32:45)
> > On Thu, Jul 23, 2020 at 7:21 PM Chris Wilson <chris@chris-wilson.co.uk>
> wrote:
> > >
> > > An unfortunate sequence of events, but it turns out there is a valid
> > > usecase for being able to free/decouple the driver objects before
> > > they are freed by the DRM core. In particular, if we have a pointer
> > > into a drm core object from inside a driver object, that pointer
> > > needs to be nerfed *before* it is freed so that concurrent access
> > > (e.g. debugfs) does not following the dangling pointer.
> > >
> > > The legacy marker was adding in the code movement from drp_fops.c to
> > > drm_file.c
> >
> > I might fumble a lot, but not this one:
> >
> > commit 45c3d213a400c952ab7119f394c5293bb6877e6b
> > Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Date:   Mon May 8 10:26:33 2017 +0200
> >
> >     drm: Nerf the preclose callback for modern drivers
> 
> Gah, when I going through the history it looked like it appeared out of
> nowhere.
> 
> > Also looking at the debugfs hook that has some rather adventurous
> > stuff going on I think, feels a bit like a kitchensink with batteries
> > included. If that's really all needed I'd say iterate the contexts by
> > first going over files, then the ctx (which arent shared anyway) and
> > the problem should also be gone.
> 
> Or we could cut out the middlelayer and put the release under the driver
> control with a call to the drm_release() when the driver is ready.

Chiris, can explain this idea, or post a patch ?

--CQ

> -Chris
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