Re: [PATCH 2/5] drm/vblank: Introduce deferred vblank enable/disable

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

Hi,

kernel test robot noticed the following build warnings:

[auto build test WARNING on drm-misc/drm-misc-next]
[also build test WARNING on daeinki-drm-exynos/exynos-drm-next drm/drm-next drm-i915/for-linux-next-fixes drm-tip/drm-tip linus/master v7.0-rc1 next-20260224]
[cannot apply to drm-i915/for-linux-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/sunpeng-li-amd-com/drm-vblank-Add-drm_crtc_vblank_is_off-helper/20260225-052945
base:   https://gitlab.freedesktop.org/drm/misc/kernel.git drm-misc-next
patch link:    https://lore.kernel.org/r/20260224212639.390768-3-sunpeng.li%40amd.com
patch subject: [PATCH 2/5] drm/vblank: Introduce deferred vblank enable/disable
config: microblaze-randconfig-r053-20260225 (https://download.01.org/0day-ci/archive/20260225/202602251257.hwgG2w64-lkp@intel.com/config)
compiler: microblaze-linux-gcc (GCC) 8.5.0

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/202602251257.hwgG2w64-lkp@intel.com/

cocci warnings: (new ones prefixed by >>)
>> drivers/gpu/drm/drm_vblank.c:1402:6-25: WARNING: atomic_dec_and_test variation before object free at line 1409.
   drivers/gpu/drm/drm_vblank.c:1402:6-25: WARNING: atomic_dec_and_test variation before object free at line 1416.

vim +1402 drivers/gpu/drm/drm_vblank.c

  1385	
  1386	void drm_vblank_put(struct drm_device *dev, unsigned int pipe)
  1387	{
  1388		struct drm_vblank_crtc *vblank = drm_vblank_crtc(dev, pipe);
  1389		int vblank_offdelay = vblank->config.offdelay_ms;
  1390		bool needs_deferred_disable;
  1391	
  1392		if (drm_WARN_ON(dev, pipe >= dev->num_crtcs))
  1393			return;
  1394	
  1395		if (drm_WARN_ON(dev, atomic_read(&vblank->refcount) == 0))
  1396			return;
  1397	
  1398		needs_deferred_disable =
  1399			drm_crtc_needs_deferred_vblank(drm_crtc_from_index(dev, pipe));
  1400	
  1401		/* Last user schedules interrupt disable */
> 1402		if (!atomic_dec_and_test(&vblank->refcount))
  1403			return;
  1404	
  1405		if (!vblank_offdelay)
  1406			return;
  1407		else if (vblank_offdelay < 0) {
  1408			if (needs_deferred_disable)
> 1409				mod_delayed_work(dev->deferred_vblank_wq,
  1410						 &vblank->disable_work,
  1411						 0);
  1412			else
  1413				vblank_disable_fn(&vblank->disable_timer);
  1414		} else if (!vblank->config.disable_immediate) {
  1415			if (needs_deferred_disable)
  1416				mod_delayed_work(dev->deferred_vblank_wq,
  1417						 &vblank->disable_work,
  1418						 msecs_to_jiffies(vblank_offdelay));
  1419			else
  1420				mod_timer(&vblank->disable_timer,
  1421					  jiffies + ((vblank_offdelay * HZ) / 1000));
  1422		}
  1423	}
  1424	

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