Flushing the fbdev's shadow buffer requires vmap'ing the BO memory, which
in turn requires pinning the BO. While being pinned, the BO cannot be moved
into VRAM for scanout. Consequently, a concurrent modeset operation that
involves the fbdev framebuffer would likely fail.
Resolve this problem be acquiring the modeset lock of the planes that use
the fbdev framebuffer. On non-atomic drivers, also acquire the mode-config
lock. This serializes the flushing of the framebuffer with concurrent
modeset operations.
v2:
* only acquire struct drm_fb_helper.lock in damage blitter (Daniel,
Christian)
Signed-off-by: Thomas Zimmermann <tzimmerm...@suse.de>
---
drivers/gpu/drm/drm_fb_helper.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index d972ce75d180..6f2763467e99 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -398,16 +398,32 @@ static int drm_fb_helper_damage_blit(struct drm_fb_helper
*fb_helper,
struct dma_buf_map map, dst;
int ret;
+ /*
+ * We have to pin the client buffer to its current location while
+ * flushing the shadow buffer. In the general case, concurrent
+ * modesetting operations could try to move the buffer and would
+ * fail. The modeset has to be serialized by acquiring the reservation
+ * object of the underlying BO here.
+ *
+ * For fbdev emulation, we only have to protect against fbdev modeset
+ * operations. Nothing else will involve the client buffer's BO. So it
+ * is sufficient to acquire struct drm_fb_helper.lock here.
+ */
+ mutex_lock(&fb_helper->lock);
+
ret = drm_client_buffer_vmap(buffer, &map);
if (ret)
- return ret;
+ goto out;
dst = map;
drm_fb_helper_damage_blit_real(fb_helper, clip, &dst);
drm_client_buffer_vunmap(buffer);
- return 0;
+out:
+ mutex_unlock(&fb_helper->lock);
+
+ return ret;
}
static void drm_fb_helper_damage_work(struct work_struct *work)
--
2.29.2
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