xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

drm: serialize drm_file.master with a new spinlock

Browse Source 
[ Upstream commit 0b0860a3cf5eccf183760b1177a1dcdb821b0b66 ]

Currently, drm_file.master pointers should be protected by
drm_device.master_mutex when being dereferenced. This is because
drm_file.master is not invariant for the lifetime of drm_file. If
drm_file is not the creator of master, then drm_file.is_master is
false, and a call to drm_setmaster_ioctl will invoke
drm_new_set_master, which then allocates a new master for drm_file and
puts the old master.

Thus, without holding drm_device.master_mutex, the old value of
drm_file.master could be freed while it is being used by another
concurrent process.

However, it is not always possible to lock drm_device.master_mutex to
dereference drm_file.master. Through the fbdev emulation code, this
might occur in a deep nest of other locks. But drm_device.master_mutex
is also the outermost lock in the nesting hierarchy, so this leads to
potential deadlocks.

To address this, we introduce a new spin lock at the bottom of the
lock hierarchy that only serializes drm_file.master. With this change,
the value of drm_file.master changes only when both
drm_device.master_mutex and drm_file.master_lookup_lock are
held. Hence, any process holding either of those locks can ensure that
the value of drm_file.master will not change concurrently.

Since no lock depends on the new drm_file.master_lookup_lock, when
drm_file.master is dereferenced, but drm_device.master_mutex cannot be
held, we can safely protect the master pointer with
drm_file.master_lookup_lock.

Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210712043508.11584-5-desmondcheongzx@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Desmond Cheong Zhi Xi
2021-07-12 12:35:07 +08:00
committed by Greg Kroah-Hartman
parent 54e51d288b
commit 06a553a99b
3 changed files with 21 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
drivers/gpu/drm/drm_file.c
View File

@@ -177,6 +177,7 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor)
init_waitqueue_head(&file->event_wait);
file->event_space = 4096; /* set aside 4k for event buffer */
spin_lock_init(&file->master_lookup_lock);
mutex_init(&file->event_read_lock);
if (drm_core_check_feature(dev, DRIVER_GEM))