[superm1:superm1/backlight-property-v5 3/21] drivers/gpu/drm/drm_vblank.c:1412:6-25: WARNING: atomic_dec_and_test variation before object free at line 1419.

[kernel test robot <lkp@intel.com>]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/superm1/linux.git superm1/backlight-property-v5
head:   5f2330560c00d587cd173ee4222011b62e1ac567
commit: eaf99ccba37426aac11866ffb268bd6b68417b00 [3/21] drm/vblank: Introduce deferred vblank enable/disable
config: sh-randconfig-r052-20260601 (https://download.01.org/0day-ci/archive/20260601/202606012258.f60EpMuU-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 10.5.0

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202606012258.f60EpMuU-lkp@intel.com/

cocci warnings: (new ones prefixed by >>)
>> drivers/gpu/drm/drm_vblank.c:1412:6-25: WARNING: atomic_dec_and_test variation before object free at line 1419.
   drivers/gpu/drm/drm_vblank.c:1412:6-25: WARNING: atomic_dec_and_test variation before object free at line 1426.

vim +1412 drivers/gpu/drm/drm_vblank.c

  1395	
  1396	void drm_vblank_put(struct drm_device *dev, unsigned int pipe)
  1397	{
  1398		struct drm_vblank_crtc *vblank = drm_vblank_crtc(dev, pipe);
  1399		int vblank_offdelay = vblank->config.offdelay_ms;
  1400		bool needs_deferred_disable;
  1401	
  1402		if (drm_WARN_ON(dev, pipe >= dev->num_crtcs))
  1403			return;
  1404	
  1405		if (drm_WARN_ON(dev, atomic_read(&vblank->refcount) == 0))
  1406			return;
  1407	
  1408		needs_deferred_disable =
  1409			drm_crtc_needs_deferred_vblank(drm_crtc_from_index(dev, pipe));
  1410	
  1411		/* Last user schedules interrupt disable */
> 1412		if (!atomic_dec_and_test(&vblank->refcount))
  1413			return;
  1414	
  1415		if (!vblank_offdelay)
  1416			return;
  1417		else if (vblank_offdelay < 0) {
  1418			if (needs_deferred_disable)
> 1419				mod_delayed_work(dev->deferred_vblank_wq,
  1420						 &vblank->disable_work,
  1421						 0);
  1422			else
  1423				vblank_disable_fn(&vblank->disable_timer);
  1424		} else if (!vblank->config.disable_immediate) {
  1425			if (needs_deferred_disable)
  1426				mod_delayed_work(dev->deferred_vblank_wq,
  1427						 &vblank->disable_work,
  1428						 msecs_to_jiffies(vblank_offdelay));
  1429			else
  1430				mod_timer(&vblank->disable_timer,
  1431					  jiffies + ((vblank_offdelay * HZ) / 1000));
  1432		}
  1433	}
  1434	

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