github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-06-07 05:55:44 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

drm: serialize drm_file.master with a new spinlock

Browse Source 
[ Upstream commit 0b0860a3cf ]

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
drivers/gpu/drm/drm_auth.c
View File

@ -135,16 +135,18 @@ static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv,
static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
{ {
struct drm_master *old_master; struct drm_master *old_master;
struct drm_master *new_master;
lockdep_assert_held_once(&dev->master_mutex); lockdep_assert_held_once(&dev->master_mutex);
WARN_ON(fpriv->is_master); WARN_ON(fpriv->is_master);
old_master = fpriv->master; old_master = fpriv->master;
fpriv->master = drm_master_create(dev); new_master = drm_master_create(dev);
if (!fpriv->master) { if (!new_master)
fpriv->master = old_master;
return -ENOMEM; return -ENOMEM;
} spin_lock(&fpriv->master_lookup_lock);
fpriv->master = new_master;
spin_unlock(&fpriv->master_lookup_lock);
fpriv->is_master = 1; fpriv->is_master = 1;
fpriv->authenticated = 1; fpriv->authenticated = 1;
@ -302,10 +304,13 @@ int drm_master_open(struct drm_file *file_priv)
/* if there is no current master make this fd it, but do not create /* if there is no current master make this fd it, but do not create
* any master object for render clients */ * any master object for render clients */
mutex_lock(&dev->master_mutex); mutex_lock(&dev->master_mutex);
if (!dev->master) if (!dev->master) {
ret = drm_new_set_master(dev, file_priv); ret = drm_new_set_master(dev, file_priv);
else } else {
spin_lock(&file_priv->master_lookup_lock);
file_priv->master = drm_master_get(dev->master); file_priv->master = drm_master_get(dev->master);
spin_unlock(&file_priv->master_lookup_lock);
}
mutex_unlock(&dev->master_mutex); mutex_unlock(&dev->master_mutex);
return ret; return ret;

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); init_waitqueue_head(&file->event_wait);
file->event_space = 4096; /* set aside 4k for event buffer */ file->event_space = 4096; /* set aside 4k for event buffer */
spin_lock_init(&file->master_lookup_lock);
mutex_init(&file->event_read_lock); mutex_init(&file->event_read_lock);
if (drm_core_check_feature(dev, DRIVER_GEM)) if (drm_core_check_feature(dev, DRIVER_GEM))

12
include/drm/drm_file.h
View File

@ -226,15 +226,21 @@ struct drm_file {
/** /**
* @master: * @master:
* *
* Master this node is currently associated with. Only relevant if * Master this node is currently associated with. Protected by struct
* drm_is_primary_client() returns true. Note that this only * &drm_device.master_mutex, and serialized by @master_lookup_lock.
* matches &drm_device.master if the master is the currently active one. *
* Only relevant if drm_is_primary_client() returns true. Note that
* this only matches &drm_device.master if the master is the currently
* active one.
* *
* See also @authentication and @is_master and the :ref:`section on * See also @authentication and @is_master and the :ref:`section on
* primary nodes and authentication <drm_primary_node>`. * primary nodes and authentication <drm_primary_node>`.
*/ */
struct drm_master *master; struct drm_master *master;
/** @master_lock: Serializes @master. */
spinlock_t master_lookup_lock;
/** @pid: Process that opened this file. */ /** @pid: Process that opened this file. */
struct pid *pid; struct pid *pid;