[PATCH] drm/i915: fix up locking inconsistency around gem_do_init

[PATCH] drm/i915: fix up locking inconsistency around gem_do_init

[Daniel Vetter]

The locking in our setup and teardown paths is rather arbitrary, but
generally we try to protect gem stuff with dev->struct_mutex. Further,
the ums/gem ioctl to setup gem _does_ take the look. So fix up this
benign inconsistency.

Notice while reading through code.

Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_dma.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 448848c..51bbd03 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1196,6 +1196,7 @@ static int i915_load_gem_init(struct drm_device *dev)
 	/* Basic memrange allocator for stolen space */
 	drm_mm_init(&dev_priv->mm.stolen, 0, prealloc_size);
 
+	mutex_lock(&dev->struct_mutex);
 	/* Let GEM Manage all of the aperture.
 	 *
 	 * However, leave one page at the end still bound to the scratch page.
@@ -1207,7 +1208,6 @@ static int i915_load_gem_init(struct drm_device *dev)
 	 */
 	i915_gem_do_init(dev, 0, mappable_size, gtt_size - PAGE_SIZE);
 
-	mutex_lock(&dev->struct_mutex);
 	ret = i915_gem_init_ringbuffer(dev);
 	mutex_unlock(&dev->struct_mutex);
 	if (ret)
-- 
1.7.8.3

Re: [PATCH] drm/i915: fix up locking inconsistency around gem_do_init

[Chris Wilson]

On Thu, 26 Jan 2012 11:41:11 +0100, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> The locking in our setup and teardown paths is rather arbitrary, but
> generally we try to protect gem stuff with dev->struct_mutex. Further,
> the ums/gem ioctl to setup gem _does_ take the look. So fix up this
> benign inconsistency.

It is completely arbitrary and only exists to keep lockdep and various
BUG_ON(mutex_lock) happy. From your reading, we would have a lockdep
warning with ums/gem?

The extra little step towards consistency is likely to save a warning
later, so
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

Re: [PATCH] drm/i915: fix up locking inconsistency around gem_do_init

[Daniel Vetter]

On Thu, Jan 26, 2012 at 01:42:02PM +0000, Chris Wilson wrote:
> On Thu, 26 Jan 2012 11:41:11 +0100, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > The locking in our setup and teardown paths is rather arbitrary, but
> > generally we try to protect gem stuff with dev->struct_mutex. Further,
> > the ums/gem ioctl to setup gem _does_ take the look. So fix up this
> > benign inconsistency.
> 
> It is completely arbitrary and only exists to keep lockdep and various
> BUG_ON(mutex_lock) happy. From your reading, we would have a lockdep
> warning with ums/gem?
> 
> The extra little step towards consistency is likely to save a warning
> later, so
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

Actually no lockdep splat to be expected, because gem_do_init is _really_
simple. But maybe we'll extend the gtt_clear stuff in there to be more
involved and this could indeed change. But currently the only reason for
that change is to satisfy my ocd ;-)
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48

Re: [PATCH] drm/i915: fix up locking inconsistency around gem_do_init

[Daniel Vetter]

On Thu, Jan 26, 2012 at 01:42:02PM +0000, Chris Wilson wrote:
> On Thu, 26 Jan 2012 11:41:11 +0100, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > The locking in our setup and teardown paths is rather arbitrary, but
> > generally we try to protect gem stuff with dev->struct_mutex. Further,
> > the ums/gem ioctl to setup gem _does_ take the look. So fix up this
> > benign inconsistency.
> 
> It is completely arbitrary and only exists to keep lockdep and various
> BUG_ON(mutex_lock) happy. From your reading, we would have a lockdep
> warning with ums/gem?
> 
> The extra little step towards consistency is likely to save a warning
> later, so
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Queued for -next, thanks for the review.
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48