[PATCH v6 7/7] drm: remove drm_file.master_lookup_lock

From: Desmond Cheong Zhi Xi
Date: Wed Aug 25 2021 - 06:27:42 EST

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In reply to: Desmond Cheong Zhi Xi: "[PATCH v6 6/7] drm: avoid circular locks with modeset_mutex and master_rwsem"
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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@xxxxxxxxx>
---
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);
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);
file_priv->master = drm_master_get(dev->master);
- spin_unlock(&file_priv->master_lookup_lock);
}
up_write(&dev->master_rwsem);

@@ -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

Next message: Barry Song: "[PATCH v3 2/3] PCI/sysfs: Don't depend on pci_dev.irq for IRQ entry"
Previous message: Barry Song: "[PATCH v3 1/3] Documentation: ABI: sysfs-bus-pci: Add description for IRQ entry"
In reply to: Desmond Cheong Zhi Xi: "[PATCH v6 6/7] drm: avoid circular locks with modeset_mutex and master_rwsem"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]