drm/crc-debugfs: User irqsafe spinlock in drm_crtc_add_crc_entry

We can be called from any context, we need to be prepared.

Noticed this while hacking on vkms, which calls this function from a
normal worker. Which really upsets lockdep.

Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Emil Velikov <emil.velikov@collabora.com>
Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190605194556.16744-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_debugfs_crc.c

@@ -396,8 +396,9 @@ int drm_crtc_add_crc_entry(struct drm_crtc *crtc, bool has_frame,
 	struct drm_crtc_crc *crc = &crtc->crc;
 	struct drm_crtc_crc_entry *entry;
 	int head, tail;
+	unsigned long flags;
 
-	spin_lock(&crc->lock);
+	spin_lock_irqsave(&crc->lock, flags);
 
 	/* Caller may not have noticed yet that userspace has stopped reading */
 	if (!crc->entries) {
@@ -428,7 +429,7 @@ int drm_crtc_add_crc_entry(struct drm_crtc *crtc, bool has_frame,
 	head = (head + 1) & (DRM_CRC_ENTRIES_NR - 1);
 	crc->head = head;
 
-	spin_unlock(&crc->lock);
+	spin_unlock_irqrestore(&crc->lock, flags);
 
 	wake_up_interruptible(&crc->wq);