All of lore.kernel.org
 help / color / mirror / Atom feed
From: Chris Wilson <chris@chris-wilson.co.uk>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Julia Lawall <julia.lawall@lip6.fr>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 12/14] drm: Move master pointer from drm_minor to drm_device
Date: Wed, 15 Jun 2016 17:33:14 +0100	[thread overview]
Message-ID: <20160615163314.GB6754@nuc-i3427.alporthouse.com> (raw)
In-Reply-To: <20160615160141.GP1338@phenom.ffwll.local>

On Wed, Jun 15, 2016 at 06:01:41PM +0200, Daniel Vetter wrote:
> On Wed, Jun 15, 2016 at 01:10:35PM +0100, Chris Wilson wrote:
> > On Tue, Jun 14, 2016 at 08:51:07PM +0200, Daniel Vetter wrote:
> > > There can only be one current master, and it's for the overall device.
> > > Render/control minors don't support master-based auth at all.
> > > 
> > > This simplifies the master logic a lot, at least in my eyes: All these
> > > additional pointer chases are just confusing.
> > 
> > One master for the device, on the struct drm_device, as opposed to hidden
> > behind the first of three minors, makes sense.
> > 
> > > @@ -128,13 +128,13 @@ static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
> > >  	lockdep_assert_held_once(&dev->master_mutex);
> > >  
> > >  	/* create a new master */
> > > -	fpriv->minor->master = drm_master_create(fpriv->minor->dev);
> > > -	if (!fpriv->minor->master)
> > > +	dev->master = drm_master_create(dev);
> > > +	if (!dev->master)
> > >  		return -ENOMEM;
> > >  
> > >  	/* take another reference for the copy in the local file priv */
> > >  	old_master = fpriv->master;
> > > -	fpriv->master = drm_master_get(fpriv->minor->master);
> > > +	fpriv->master = drm_master_get(dev->master);
> > >  
> > >  	if (dev->driver->master_create) {
> > >  		ret = dev->driver->master_create(dev, fpriv->master);
> > 
> > > @@ -234,10 +234,10 @@ int drm_master_open(struct drm_file *file_priv)
> > >  	/* if there is no current master make this fd it, but do not create
> > >  	 * any master object for render clients */
> > >  	mutex_lock(&dev->master_mutex);
> > > -	if (!file_priv->minor->master)
> > > +	if (!dev->master)
> > >  		ret = drm_new_set_master(dev, file_priv);
> > >  	else
> > > -		file_priv->master = drm_master_get(file_priv->minor->master);
> > > +		file_priv->master = drm_master_get(dev->master);
> > >  	mutex_unlock(&dev->master_mutex);
> > 
> > You could take the opportunity to make this a bit simpler:
> > 
> > 	if (!READ_ONCE(dev->master)) {
> > 		int ret;
> > 
> > 		ret = 0;
> > 		mutex_lock(&dev->master_mutex);
> > 		if (!dev->master)
> > 			ret = drm_new_master(dev);
> > 		mutex_unlock(&dev->master_mutex);
> > 		if (ret)
> > 			return ret;
> > 	}
> > 
> > 	file_priv->master = drm_master_get(dev->master);
> 
> drm_master_get(dev->master) must be under the master_mutex, without it we
> could race with a drm_master_put(&dev->master) and end up doing a kref_get
> when the refcount already reached 0.

Something is very fishy then. The behaviour of drm_new_master() would
appear to be to create a drm_master owned by the device, but really it is
owned by file_priv?

* checks back on drm_master

So drm_master is the authentication structure that needs to be unique to
a hierachy. So drm_new_set_master() and here really do appear backwards.

The old drm_new_set_master() makes more sense, it assigns to the
file_priv, and then performs a setmaster operation. In that ordering,
you could even do the file_priv local operation of creating the new
master structure before taking the lock to perform setmaster.


> > Just to straighten out the kref dance.
> > 
> > >  
> > >  	return ret;
> > > @@ -271,11 +271,11 @@ void drm_master_release(struct drm_file *file_priv)
> > >  		mutex_unlock(&dev->struct_mutex);
> > >  	}
> > >  
> > > -	if (file_priv->minor->master == file_priv->master) {
> > > +	if (dev->master == file_priv->master) {
> > >  		/* drop the reference held my the minor */
> > >  		if (dev->driver->master_drop)
> > >  			dev->driver->master_drop(dev, file_priv, true);
> > > -		drm_master_put(&file_priv->minor->master);
> > > +		drm_master_put(&dev->master);
> > 
> > This still makes me uneasy. This is not equivalent to dropmaster_ioctl
> > and subsequent setmaster_ioctl will fail as dev->master is still
> > assigned (but the owner has gone).
> 
> drm_master_put clears the pointer passed to it, so dev->master will be set
> to NULL. And it does the same as drop_master (wrt dev->master at least,
> master_release also needs to clean up file_priv->master on top). Not sure
> it's worth it to extract those 5 lines into a __drm_drop_master() helper
> function? I can respin with that if you want. On the master_open/setmaster
> side the shared code is already extracted in drm_new_set_master().

drm_master_put() nullifies, didn't expect that.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

  reply	other threads:[~2016-06-15 16:33 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-14 18:50 [PATCH 00/14] Cruft removal around drm_master Daniel Vetter
2016-06-14 18:50 ` [PATCH 01/14] drm: Nuke legacy maps debugfs files Daniel Vetter
2016-06-15 11:23   ` Chris Wilson
2016-06-15 12:00   ` Emil Velikov
2016-06-14 18:50 ` [PATCH 02/14] drm: Hide hw.lock cleanup in filp->release better Daniel Vetter
2016-06-15 11:26   ` [Intel-gfx] " Chris Wilson
2016-06-15 12:10   ` Emil Velikov
2016-06-14 18:50 ` [PATCH 03/14] drm: Link directly from drm_master to drm_device Daniel Vetter
2016-06-15 11:29   ` Chris Wilson
2016-06-15 12:50   ` [Intel-gfx] " Emil Velikov
2016-06-15 15:45     ` Daniel Vetter
2016-06-16 20:04       ` Emil Velikov
2016-06-14 18:50 ` [PATCH 04/14] drm: Move master functions into drm_auth.c Daniel Vetter
2016-06-15 11:31   ` Chris Wilson
2016-06-15 15:47     ` Daniel Vetter
2016-06-14 18:51 ` [PATCH 05/14] drm: Extract drm_master_open Daniel Vetter
2016-06-15 11:41   ` [Intel-gfx] " Chris Wilson
2016-06-14 18:51 ` [PATCH 06/14] drm: Extract drm_master_relase Daniel Vetter
2016-06-15 11:43   ` [Intel-gfx] " Chris Wilson
2016-06-16  8:18     ` Daniel Vetter
2016-06-14 18:51 ` [PATCH 07/14] drm: Only do the hw.lock cleanup in master_relase for !MODESET Daniel Vetter
2016-06-15 11:48   ` Chris Wilson
2016-06-15 15:49     ` [Intel-gfx] " Daniel Vetter
2016-06-14 18:51 ` [PATCH 08/14] drm: Move authmagic cleanup into drm_master_release Daniel Vetter
2016-06-15 11:51   ` Chris Wilson
2016-06-14 18:51 ` [PATCH 09/14] drm: Protect authmagic with master_mutex Daniel Vetter
2016-06-15 11:54   ` [Intel-gfx] " Chris Wilson
2016-06-15 15:52     ` Daniel Vetter
2016-06-14 18:51 ` [PATCH 10/14] drm: Mark authmagic ioctls as unlocked Daniel Vetter
2016-06-15 11:55   ` [Intel-gfx] " Chris Wilson
2016-06-14 18:51 ` [PATCH 11/14] drm: Mark set/drop master ioctl " Daniel Vetter
2016-06-15 11:56   ` [Intel-gfx] " Chris Wilson
2016-06-14 18:51 ` [PATCH 12/14] drm: Move master pointer from drm_minor to drm_device Daniel Vetter
2016-06-15 12:10   ` [Intel-gfx] " Chris Wilson
2016-06-15 16:01     ` Daniel Vetter
2016-06-15 16:33       ` Chris Wilson [this message]
2016-06-15 19:54         ` [Intel-gfx] " Daniel Vetter
2016-06-14 18:51 ` [PATCH 13/14] drm: Clean up drm_crtc.h Daniel Vetter
2016-06-14 18:51 ` [PATCH 14/14] drm: Use dev->name as fallback for dev->unique Daniel Vetter
2016-06-15  5:42 ` ✓ Ro.CI.BAT: success for Cruft removal around drm_master Patchwork

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20160615163314.GB6754@nuc-i3427.alporthouse.com \
    --to=chris@chris-wilson.co.uk \
    --cc=daniel.vetter@ffwll.ch \
    --cc=daniel.vetter@intel.com \
    --cc=daniel@ffwll.ch \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=intel-gfx@lists.freedesktop.org \
    --cc=julia.lawall@lip6.fr \
    --subject='Re: [PATCH 12/14] drm: Move master pointer from drm_minor to drm_device' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.