From 32228ff5f7e1b1c8916e811d525b6e15e3d21b3d Mon Sep 17 00:00:00 2001 From: Thomas Zimmermann Date: Fri, 20 Nov 2020 11:25:45 +0100 Subject: [PATCH] drm/fb-helper: Acquire modeset lock around shadow-buffer flushing 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 Acked-by: Maxime Ripard Acked-by: Sam Ravnborg Link: https://patchwork.freedesktop.org/patch/msgid/20201120102545.4047-11-tzimmermann@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 0aac545..4b81195 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) -- 2.7.4