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drm/gem: Acquire references on GEM handles for framebuffers

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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.

Commit 1a148af060 ("drm/gem-shmem: Use dma_buf from GEM object
instance") triggers the segmentation fault easily by using the dma-buf
field more widely. The underlying issue with reference counting has
been present before.

v2:
- acquire the handle instead of the BO (Christian)
- fix comment style (Christian)
- drop the Fixes tag (Christian)
- rename err_ gotos
- add missing Link tag

Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://elixir.bootlin.com/linux/v6.15/source/drivers/gpu/drm/drm_gem.c#L241 # [1]
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>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20250630084001.293053-1-tzimmermann@suse.de
This commit is contained in:
Thomas Zimmermann 2025-06-30 10:36:47 +02:00
parent 8af39ec5cf
commit 5307dce878
3 changed files with 51 additions and 11 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

44
drivers/gpu/drm/drm_gem.c
View file

@ -212,6 +212,35 @@ 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.
@ -242,8 +271,14 @@ 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;
@ -268,6 +303,7 @@ 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
@ -389,8 +425,8 @@ 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

16
drivers/gpu/drm/drm_gem_framebuffer_helper.c
View file

@ -99,7 +99,7 @@ void drm_gem_fb_destroy(struct drm_framebuffer *fb)
unsigned int i;
for (i = 0; i < fb->format->num_planes; i++)
drm_gem_object_put(fb->obj[i]);
drm_gem_object_handle_put_unlocked(fb->obj[i]);
drm_framebuffer_cleanup(fb);
kfree(fb);
@ -182,8 +182,10 @@ int drm_gem_fb_init_with_funcs(struct drm_device *dev,
if (!objs[i]) {
drm_dbg_kms(dev, "Failed to lookup GEM object\n");
ret = -ENOENT;
goto err_gem_object_put;
goto err_gem_object_handle_put_unlocked;
}
drm_gem_object_handle_get_unlocked(objs[i]);
drm_gem_object_put(objs[i]);
min_size = (height - 1) * mode_cmd->pitches[i]
+ drm_format_info_min_pitch(info, i, width)
@ -193,22 +195,22 @@ int drm_gem_fb_init_with_funcs(struct drm_device *dev,
drm_dbg_kms(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;
goto err_gem_object_handle_put_unlocked;
}
}
ret = drm_gem_fb_init(dev, fb, mode_cmd, objs, i, funcs);
if (ret)
goto err_gem_object_put;
goto err_gem_object_handle_put_unlocked;
return 0;
err_gem_object_put:
err_gem_object_handle_put_unlocked:
while (i > 0) {
--i;
drm_gem_object_put(objs[i]);
drm_gem_object_handle_put_unlocked(objs[i]);
}
return ret;
}

2
drivers/gpu/drm/drm_internal.h
View file

@ -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);