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Revert "drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference"

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This reverts commit:

  fa7d81bb3c ("drm/fb-helper: Reduce READ_ONCE(master) to lockless_dereference")

As Peter explained:

  [...] lockless_dereference() is _stronger_ than READ_ONCE(), not weaker.

  [...]

  Also, clue is in the name: 'dereference', you don't actually dereference
  the pointer here, only load it.

My next patch breaks the compile without this revert, because it assumes
you want to deference and thus also need the struct type visible (which
it isn't here), so revert it.

Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1470909022-687-1-git-send-email-johannes@sipsolutions.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Johannes Berg 2016-08-11 11:50:21 +02:00 committed by Ingo Molnar
parent 3684b03d8e
commit f17b3ea3d2
1 changed files with 1 additions and 1 deletions
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2
drivers/gpu/drm/drm_fb_helper.c
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@ -464,7 +464,7 @@ static bool drm_fb_helper_is_bound(struct drm_fb_helper *fb_helper)
/* Sometimes user space wants everything disabled, so don't steal the
* display if there's a master. */
if (lockless_dereference(dev->master))
if (READ_ONCE(dev->master))
return false;
drm_for_each_crtc(crtc, dev) {