linux-kernel - [PATCH v1] drm/gem-vram: Fix deadlock in drm_gem_vram

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Date:   Mon, 14 Nov 2022 02:38:50 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dmitry Vyukov <dvyukov@...gle.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1] drm/gem-vram: Fix deadlock in drm_gem_vram_vmap()

Recently DRM framebuffer core and all drivers were moved to unlocked
vmapping functions that take the reservation lock. The drm_gem_vram_vmap()
was missed out by accident and now deadlocks drivers that use drm_gem_vram
helpers when framebuffer is updated, like Bochs driver. Remove the locking
from drm_gem_vram_v[un]map() functions to fix the deadlock.

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Fixes: 79e2cf2e7a19 ("drm/gem: Take reservation lock for vmap/vunmap operations")
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
---
 drivers/gpu/drm/drm_gem_vram_helper.c | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
index 125160b534be..b6c7e3803bb3 100644
--- a/drivers/gpu/drm/drm_gem_vram_helper.c
+++ b/drivers/gpu/drm/drm_gem_vram_helper.c
@@ -433,25 +433,19 @@ int drm_gem_vram_vmap(struct drm_gem_vram_object *gbo, struct iosys_map *map)
 {
 	int ret;
 
-	ret = ttm_bo_reserve(&gbo->bo, true, false, NULL);
-	if (ret)
-		return ret;
+	dma_resv_assert_held(gbo->bo.base.resv);
 
 	ret = drm_gem_vram_pin_locked(gbo, 0);
 	if (ret)
-		goto err_ttm_bo_unreserve;
+		return ret;
 	ret = drm_gem_vram_kmap_locked(gbo, map);
 	if (ret)
 		goto err_drm_gem_vram_unpin_locked;
 
-	ttm_bo_unreserve(&gbo->bo);
-
 	return 0;
 
 err_drm_gem_vram_unpin_locked:
 	drm_gem_vram_unpin_locked(gbo);
-err_ttm_bo_unreserve:
-	ttm_bo_unreserve(&gbo->bo);
 	return ret;
 }
 EXPORT_SYMBOL(drm_gem_vram_vmap);
@@ -467,16 +461,10 @@ EXPORT_SYMBOL(drm_gem_vram_vmap);
 void drm_gem_vram_vunmap(struct drm_gem_vram_object *gbo,
 			 struct iosys_map *map)
 {
-	int ret;
-
-	ret = ttm_bo_reserve(&gbo->bo, false, false, NULL);
-	if (WARN_ONCE(ret, "ttm_bo_reserve_failed(): ret=%d\n", ret))
-		return;
+	dma_resv_assert_held(gbo->bo.base.resv);
 
 	drm_gem_vram_kunmap_locked(gbo, map);
 	drm_gem_vram_unpin_locked(gbo);
-
-	ttm_bo_unreserve(&gbo->bo);
 }
 EXPORT_SYMBOL(drm_gem_vram_vunmap);
 
-- 
2.37.3