A GEM handle can be released while the GEM buffer object is attached to a DRM framebuffer. This leads to the release of the dma-buf backing the buffer object, if any. [1] Trying to use the framebuffer in further mode-setting operations leads to a segmentation fault. Most easily happens with driver that use shadow planes for vmap-ing the dma-buf during a page flip. An example is shown below.
[ 156.791968] ------------[ cut here ]------------ [ 156.796830] WARNING: CPU: 2 PID: 2255 at drivers/dma-buf/dma-buf.c:1527 dma_buf_vmap+0x224/0x430 [...] [ 156.942028] RIP: 0010:dma_buf_vmap+0x224/0x430 [ 157.043420] Call Trace: [ 157.045898] <TASK> [ 157.048030] ? show_trace_log_lvl+0x1af/0x2c0 [ 157.052436] ? show_trace_log_lvl+0x1af/0x2c0 [ 157.056836] ? show_trace_log_lvl+0x1af/0x2c0 [ 157.061253] ? drm_gem_shmem_vmap+0x74/0x710 [ 157.065567] ? dma_buf_vmap+0x224/0x430 [ 157.069446] ? __warn.cold+0x58/0xe4 [ 157.073061] ? dma_buf_vmap+0x224/0x430 [ 157.077111] ? report_bug+0x1dd/0x390 [ 157.080842] ? handle_bug+0x5e/0xa0 [ 157.084389] ? exc_invalid_op+0x14/0x50 [ 157.088291] ? asm_exc_invalid_op+0x16/0x20 [ 157.092548] ? dma_buf_vmap+0x224/0x430 [ 157.096663] ? dma_resv_get_singleton+0x6d/0x230 [ 157.101341] ? __pfx_dma_buf_vmap+0x10/0x10 [ 157.105588] ? __pfx_dma_resv_get_singleton+0x10/0x10 [ 157.110697] drm_gem_shmem_vmap+0x74/0x710 [ 157.114866] drm_gem_vmap+0xa9/0x1b0 [ 157.118763] drm_gem_vmap_unlocked+0x46/0xa0 [ 157.123086] drm_gem_fb_vmap+0xab/0x300 [ 157.126979] drm_atomic_helper_prepare_planes.part.0+0x487/0xb10 [ 157.133032] ? lockdep_init_map_type+0x19d/0x880 [ 157.137701] drm_atomic_helper_commit+0x13d/0x2e0 [ 157.142671] ? drm_atomic_nonblocking_commit+0xa0/0x180 [ 157.147988] drm_mode_atomic_ioctl+0x766/0xe40 [...] [ 157.346424] ---[ end trace 0000000000000000 ]---
Acquiring GEM handles for the framebuffer's GEM buffer objects prevents this from happening. The framebuffer's cleanup later puts the handle references.
The Fixes tag points to commit 1a148af06000 ("drm/gem-shmem: Use dma_buf from GEM object instance"), which triggers the segmentation fault. The issue has been present before.
Suggested-by: Christian König christian.koenig@amd.com Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 1a148af06000 ("drm/gem-shmem: Use dma_buf from GEM object instance") Cc: Thomas Zimmermann tzimmermann@suse.de Cc: Anusha Srivatsa asrivats@redhat.com Cc: Christian König christian.koenig@amd.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Sumit Semwal sumit.semwal@linaro.org Cc: "Christian König" christian.koenig@amd.com Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org Cc: stable@vger.kernel.org --- drivers/gpu/drm/drm_gem.c | 44 ++++++++++++++++++-- drivers/gpu/drm/drm_gem_framebuffer_helper.c | 7 +++- drivers/gpu/drm/drm_internal.h | 2 + 3 files changed, 48 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c index 19d50d254fe6..8be50b3cc9c2 100644 --- a/drivers/gpu/drm/drm_gem.c +++ b/drivers/gpu/drm/drm_gem.c @@ -213,6 +213,35 @@ void drm_gem_private_object_fini(struct drm_gem_object *obj) } EXPORT_SYMBOL(drm_gem_private_object_fini);
+static void drm_gem_object_handle_get(struct drm_gem_object *obj) +{ + struct drm_device *dev = obj->dev; + + drm_WARN_ON(dev, !mutex_is_locked(&dev->object_name_lock)); + + if (obj->handle_count++ == 0) + drm_gem_object_get(obj); +} + +/** + * drm_gem_object_handle_get_unlocked - acquire reference on user-space handles + * @obj: GEM object + * + * Acquires a reference on the GEM buffer object's handle. Required + * to keep the GEM object alive. Call drm_gem_object_handle_put_unlocked() + * to release the reference. + */ +void drm_gem_object_handle_get_unlocked(struct drm_gem_object *obj) +{ + struct drm_device *dev = obj->dev; + + guard(mutex)(&dev->object_name_lock); + + drm_WARN_ON(dev, !obj->handle_count); // first ref taken in create-tail helper + drm_gem_object_handle_get(obj); +} +EXPORT_SYMBOL(drm_gem_object_handle_get_unlocked); + /** * drm_gem_object_handle_free - release resources bound to userspace handles * @obj: GEM object to clean up. @@ -243,8 +272,14 @@ static void drm_gem_object_exported_dma_buf_free(struct drm_gem_object *obj) } }
-static void -drm_gem_object_handle_put_unlocked(struct drm_gem_object *obj) +/** + * drm_gem_object_handle_put_unlocked - releases reference on user-space handles + * @obj: GEM object + * + * Releases a reference on the GEM buffer object's handle. Possibly releases + * the GEM buffer object and associated dma-buf objects. + */ +void drm_gem_object_handle_put_unlocked(struct drm_gem_object *obj) { struct drm_device *dev = obj->dev; bool final = false; @@ -269,6 +304,7 @@ drm_gem_object_handle_put_unlocked(struct drm_gem_object *obj) if (final) drm_gem_object_put(obj); } +EXPORT_SYMBOL(drm_gem_object_handle_put_unlocked);
/* * Called at device or object close to release the file's @@ -390,8 +426,8 @@ drm_gem_handle_create_tail(struct drm_file *file_priv, int ret;
WARN_ON(!mutex_is_locked(&dev->object_name_lock)); - if (obj->handle_count++ == 0) - drm_gem_object_get(obj); + + drm_gem_object_handle_get(obj);
/* * Get the user-visible handle using idr. Preload and perform diff --git a/drivers/gpu/drm/drm_gem_framebuffer_helper.c b/drivers/gpu/drm/drm_gem_framebuffer_helper.c index 618ce725cd75..723f1d652c01 100644 --- a/drivers/gpu/drm/drm_gem_framebuffer_helper.c +++ b/drivers/gpu/drm/drm_gem_framebuffer_helper.c @@ -99,8 +99,10 @@ void drm_gem_fb_destroy(struct drm_framebuffer *fb) { unsigned int i;
- for (i = 0; i < fb->format->num_planes; i++) + for (i = 0; i < fb->format->num_planes; i++) { + drm_gem_object_handle_put_unlocked(fb->obj[i]); drm_gem_object_put(fb->obj[i]); + }
drm_framebuffer_cleanup(fb); kfree(fb); @@ -185,6 +187,7 @@ int drm_gem_fb_init_with_funcs(struct drm_device *dev, ret = -ENOENT; goto err_gem_object_put; } + drm_gem_object_handle_get_unlocked(objs[i]);
min_size = (height - 1) * mode_cmd->pitches[i] + drm_format_info_min_pitch(info, i, width) @@ -195,6 +198,7 @@ int drm_gem_fb_init_with_funcs(struct drm_device *dev, "GEM object size (%zu) smaller than minimum size (%u) for plane %d\n", objs[i]->size, min_size, i); drm_gem_object_put(objs[i]); + drm_gem_object_handle_put_unlocked(objs[i]); ret = -EINVAL; goto err_gem_object_put; } @@ -210,6 +214,7 @@ int drm_gem_fb_init_with_funcs(struct drm_device *dev, while (i > 0) { --i; drm_gem_object_put(objs[i]); + drm_gem_object_handle_put_unlocked(objs[i]); } return ret; } diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h index 442eb31351dd..f7b414a813ae 100644 --- a/drivers/gpu/drm/drm_internal.h +++ b/drivers/gpu/drm/drm_internal.h @@ -161,6 +161,8 @@ void drm_sysfs_lease_event(struct drm_device *dev);
/* drm_gem.c */ int drm_gem_init(struct drm_device *dev); +void drm_gem_object_handle_get_unlocked(struct drm_gem_object *obj); +void drm_gem_object_handle_put_unlocked(struct drm_gem_object *obj); int drm_gem_handle_create_tail(struct drm_file *file_priv, struct drm_gem_object *obj, u32 *handlep);