linux-kernel - drm: understanding the kernel warning during drm_vblank

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Message-ID: <6198455d-59b4-c4b0-94c1-6e0d460f2451@mentor.com>
Date:   Thu, 29 Nov 2018 19:30:45 +0500
From:   Ahsan Hussain <ahsan_hussain@...tor.com>
To:     <dri-devel@...ts.freedesktop.org>
CC:     <linux-kernel@...r.kernel.org>
Subject: drm: understanding the kernel warning during drm_vblank_cleanup()

Hi folks,

I'm new to DRM and trying to understand the warning in 
drivers/gpu/drm/drm_vblank.c during drm_vblank_cleanup().

WARN_ON(READ_ONCE(vblank->enabled) &&
     drm_core_check_feature(dev, DRIVER_MODESET));

Is the drm driver responsible for making sure that !(vblank->enabled) in 
the .unbind operation, or is this something related to userspace? What 
does the warning signify? Git history did not help here at all.

Regards,

Ahsan.