On Thu, Aug 26, 2021 at 10:01:22AM +0800, Desmond Cheong Zhi Xi wrote:
Previously, master_lookup_lock was introduced in commit 0b0860a3cf5e ("drm: serialize drm_file.master with a new spinlock") to serialize accesses to drm_file.master. This then allowed us to write drm_file_get_master in commit 56f0729a510f ("drm: protect drm_master pointers in drm_lease.c").
The rationale behind introducing a new spinlock at the time was that the other lock that could have been used (drm_device.master_mutex) was the outermost lock, so embedding calls to drm_file_get_master and drm_is_current_master in various functions easily caused us to invert the lock hierarchy.
Following the conversion of master_mutex into a rwsem, and its use to plug races with modesetting rights, we've untangled some lock hierarchies and removed the need for using drm_file_get_master and the unlocked version of drm_is_current_master in multiple places.
Hence, we can take this opportunity to clean up the locking design by replacing master_lookup_lock with drm_device.master_rwsem.
Signed-off-by: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com
drivers/gpu/drm/drm_auth.c | 19 +++++++------------ drivers/gpu/drm/drm_file.c | 1 - drivers/gpu/drm/drm_internal.h | 1 + drivers/gpu/drm/drm_ioctl.c | 4 ++-- drivers/gpu/drm/drm_lease.c | 18 ++++++++---------- include/drm/drm_file.h | 9 +-------- 6 files changed, 19 insertions(+), 33 deletions(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index f2b2f197052a..232416119407 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -61,10 +61,9 @@
- trusted clients.
*/
-static bool drm_is_current_master_locked(struct drm_file *fpriv) +bool drm_is_current_master_locked(struct drm_file *fpriv) {
- lockdep_assert_once(lockdep_is_held(&fpriv->master_lookup_lock) ||
lockdep_is_held(&fpriv->minor->dev->master_rwsem));
lockdep_assert_held_once(&fpriv->minor->dev->master_rwsem);
return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
} @@ -83,9 +82,9 @@ bool drm_is_current_master(struct drm_file *fpriv) { bool ret;
- spin_lock(&fpriv->master_lookup_lock);
- down_read(&fpriv->minor->dev->master_rwsem);
Looking at the 3 patches and the need to have a locked version of pretty much everything I'm wondering: Can't we just drop the spinlock completely, and everywhere we've taking it thus far replace it with a lockdep_assert_held_once?
The thing is, if there's any path left that doesn't hold the rwsem in at least read mode we have a bug. And the right way to fix such a bug is to grab the rwsem sufficiently high up in the callchain. That way I think we should be able to avoid all these tedious changes to everything, including touching i915 and vmwgfx drivers.
Or am I missing something big time? -Daniel
ret = drm_is_current_master_locked(fpriv);
- spin_unlock(&fpriv->master_lookup_lock);
up_read(&fpriv->minor->dev->master_rwsem);
return ret;
} @@ -120,7 +119,7 @@ int drm_authmagic(struct drm_device *dev, void *data, DRM_DEBUG("%u\n", auth->magic);
down_write(&dev->master_rwsem);
- if (unlikely(!drm_is_current_master(file_priv))) {
- if (unlikely(!drm_is_current_master_locked(file_priv))) { up_write(&dev->master_rwsem); return -EACCES; }
@@ -178,9 +177,7 @@ static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) new_master = drm_master_create(dev); if (!new_master) return -ENOMEM;
spin_lock(&fpriv->master_lookup_lock); fpriv->master = new_master;
spin_unlock(&fpriv->master_lookup_lock);
fpriv->is_master = 1; fpriv->authenticated = 1;
@@ -343,9 +340,7 @@ int drm_master_open(struct drm_file *file_priv) if (!dev->master) { ret = drm_new_set_master(dev, file_priv); } else {
spin_lock(&file_priv->master_lookup_lock);spin_unlock(&file_priv->master_lookup_lock);@@ -413,13 +408,13 @@ struct drm_master *drm_file_get_master(struct drm_file *file_priv) if (!file_priv) return NULL;
- spin_lock(&file_priv->master_lookup_lock);
- down_read(&file_priv->minor->dev->master_rwsem); if (!file_priv->master) goto unlock; master = drm_master_get(file_priv->master);
unlock:
- spin_unlock(&file_priv->master_lookup_lock);
- up_read(&file_priv->minor->dev->master_rwsem); return master;
} EXPORT_SYMBOL(drm_file_get_master); diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c index 90b62f360da1..8c846e0179d7 100644 --- a/drivers/gpu/drm/drm_file.c +++ b/drivers/gpu/drm/drm_file.c @@ -176,7 +176,6 @@ 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))
diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h index 17f3548c8ed2..5d421f749a17 100644 --- a/drivers/gpu/drm/drm_internal.h +++ b/drivers/gpu/drm/drm_internal.h @@ -132,6 +132,7 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data, struct drm_file *filp);
/* drm_auth.c */ +bool drm_is_current_master_locked(struct drm_file *fpriv); int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv); int drm_authmagic(struct drm_device *dev, void *data, diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c index 8bea39ffc5c0..c728437466c3 100644 --- a/drivers/gpu/drm/drm_ioctl.c +++ b/drivers/gpu/drm/drm_ioctl.c @@ -386,7 +386,7 @@ static int drm_setversion(struct drm_device *dev, void *data, struct drm_file *f int if_version, retcode = 0;
down_write(&dev->master_rwsem);
- if (unlikely(!drm_is_current_master(file_priv))) {
- if (unlikely(!drm_is_current_master_locked(file_priv))) { retcode = -EACCES; goto unlock; }
@@ -540,7 +540,7 @@ static int drm_ioctl_permit(u32 flags, struct drm_file *file_priv)
/* MASTER is only for master or control clients */ if (unlikely((flags & DRM_MASTER) &&
!drm_is_current_master(file_priv)))
!drm_is_current_master_locked(file_priv)))return -EACCES;
/* Render clients must be explicitly allowed */
diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c index 15bf3a3c76d1..0eecf320b1ab 100644 --- a/drivers/gpu/drm/drm_lease.c +++ b/drivers/gpu/drm/drm_lease.c @@ -498,12 +498,12 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, return PTR_ERR(lessee_file);
down_read(&dev->master_rwsem);
- if (unlikely(!drm_is_current_master(lessor_priv))) {
- if (unlikely(!drm_is_current_master_locked(lessor_priv))) { ret = -EACCES; goto out_file; }
- lessor = drm_file_get_master(lessor_priv);
- lessor = lessor_priv->master; /* Do not allow sub-leases */ if (lessor->lessor) { DRM_DEBUG_LEASE("recursive leasing not allowed\n");
@@ -565,7 +565,6 @@ int drm_mode_create_lease_ioctl(struct drm_device *dev, /* Hook up the fd */ fd_install(fd, lessee_file);
- drm_master_put(&lessor); up_read(&dev->master_rwsem); DRM_DEBUG_LEASE("drm_mode_create_lease_ioctl succeeded\n"); return 0;
@@ -600,7 +599,8 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP;
- lessor = drm_file_get_master(lessor_priv);
lockdep_assert_held_once(&dev->master_rwsem);
lessor = lessor_priv->master; DRM_DEBUG_LEASE("List lessees for %d\n", lessor->lessee_id);
mutex_lock(&dev->mode_config.idr_mutex);
@@ -624,7 +624,6 @@ int drm_mode_list_lessees_ioctl(struct drm_device *dev, arg->count_lessees = count;
mutex_unlock(&dev->mode_config.idr_mutex);
drm_master_put(&lessor);
return ret;
} @@ -650,7 +649,8 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP;
- lessee = drm_file_get_master(lessee_priv);
lockdep_assert_held_once(&dev->master_rwsem);
lessee = lessee_priv->master; DRM_DEBUG_LEASE("get lease for %d\n", lessee->lessee_id);
mutex_lock(&dev->mode_config.idr_mutex);
@@ -678,7 +678,6 @@ int drm_mode_get_lease_ioctl(struct drm_device *dev, arg->count_objects = count;
mutex_unlock(&dev->mode_config.idr_mutex);
drm_master_put(&lessee);
return ret;
} @@ -703,11 +702,11 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev, return -EOPNOTSUPP;
down_write(&dev->master_rwsem);
- if (unlikely(!drm_is_current_master(lessor_priv))) {
- if (unlikely(!drm_is_current_master_locked(lessor_priv))) { ret = -EACCES; goto unlock; }
- lessor = drm_file_get_master(lessor_priv);
lessor = lessor_priv->master; mutex_lock(&dev->mode_config.idr_mutex);
lessee = _drm_find_lessee(lessor, arg->lessee_id);
@@ -728,7 +727,6 @@ int drm_mode_revoke_lease_ioctl(struct drm_device *dev,
fail: mutex_unlock(&dev->mode_config.idr_mutex);
- drm_master_put(&lessor);
unlock: up_write(&dev->master_rwsem); diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h index d12bb2ba7814..e2d49fe3e32d 100644 --- a/include/drm/drm_file.h +++ b/include/drm/drm_file.h @@ -227,16 +227,12 @@ struct drm_file { * @master: * * Master this node is currently associated with. Protected by struct
* &drm_device.master_rwsem, and serialized by @master_lookup_lock.
* &drm_device.master_rwsem.
- 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.
* To update @master, both &drm_device.master_rwsem and* @master_lookup_lock need to be held, therefore holding either of* them is safe and enough for the read side.*
- When dereferencing this pointer, either hold struct
- &drm_device.master_rwsem for the duration of the pointer's use, or
- use drm_file_get_master() if struct &drm_device.master_rwsem is not
@@ -248,9 +244,6 @@ struct drm_file { */ struct drm_master *master;
- /** @master_lock: Serializes @master. */
- spinlock_t master_lookup_lock;
- /** @pid: Process that opened this file. */ struct pid *pid;
-- 2.25.1