drm/i915: Fix up usage of SHRINK_STOP

In

commit 81e49f811404f428a9d9a63295a0c267e802fa12
Author: Glauber Costa <[e-mail]>
Date: Wed Aug 28 10:18:13 2013 +1000

i915: bail out earlier when shrinker cannot acquire mutex

SHRINK_STOP was added to tell the core shrinker code to bail out and
go to the next shrinker since the i915 shrinker couldn't acquire
required locks. But the SHRINK_STOP return code was added to the
->count_objects callback and not the ->scan_objects callback as it
should have been, resulting in tons of dmesg noise like

shrink_slab: i915_gem_inactive_scan+0x0/0x9c negative objects to delete nr=-xxxxxxxxx

Fix discusssed with Dave Chinner.

References: http://www.spinics.net/lists/intel-gfx/msg33597.html
Reported-by: Knut Petersen <[e-mail]>
Cc: Knut Petersen <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Cc: Glauber Costa <[e-mail]>
Cc: Glauber Costa <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Acked-by: Dave Chinner <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>

drivers/gpu/drm/i915/i915_gem.c

···
 
 	if (!mutex_trylock(&dev->struct_mutex)) {
 		if (!mutex_is_locked_by(&dev->struct_mutex, current))
-			return SHRINK_STOP;
+			return 0;
 
 		if (dev_priv->mm.shrinker_no_lock_stealing)
-			return SHRINK_STOP;
+			return 0;
 
 		unlock = false;
 	}
···
 
 	if (!mutex_trylock(&dev->struct_mutex)) {
 		if (!mutex_is_locked_by(&dev->struct_mutex, current))
-			return 0;
+			return SHRINK_STOP;
 
 		if (dev_priv->mm.shrinker_no_lock_stealing)
-			return 0;
+			return SHRINK_STOP;
 
 		unlock = false;
 	}