| Message ID | 20210818073824.1560124-6-desmondcheongzx@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm, kernel: update locking for DRM | expand |
On Wed, Aug 18, 2021 at 03:38:20PM +0800, Desmond Cheong Zhi Xi wrote: > Currently, drm_device.master_mutex is used to serialize writes to the > drm_master.magic_map idr and to protect drm_master.unique{_len}. > > In preparation for converting drm_device.master_mutex into an outer > rwsem that might be read locked before entering some of these > functions, we can instead serialize access to drm_master.magic_map and > drm_master.unique{_len} using drm_device.master_lookup_lock which is > an inner lock. > > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> > --- > drivers/gpu/drm/drm_auth.c | 12 +++++++----- > drivers/gpu/drm/drm_ioctl.c | 10 ++++++---- > include/drm/drm_auth.h | 6 +++--- > include/drm/drm_device.h | 7 ++++++- > 4 files changed, 22 insertions(+), 13 deletions(-) > > diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c > index b7230604496b..0acb444fbbac 100644 > --- a/drivers/gpu/drm/drm_auth.c > +++ b/drivers/gpu/drm/drm_auth.c > @@ -98,10 +98,10 @@ int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv) > struct drm_master *master; > int ret = 0; > > - mutex_lock(&dev->master_mutex); > + spin_lock(&dev->master_lookup_lock); > master = file_priv->master; > if (!master) { > - mutex_unlock(&dev->master_mutex); > + spin_unlock(&dev->master_lookup_lock); > return -EINVAL; > } > > @@ -112,7 +112,7 @@ int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv) > file_priv->magic = ret; > } > auth->magic = file_priv->magic; > - mutex_unlock(&dev->master_mutex); > + spin_unlock(&dev->master_lookup_lock); > > DRM_DEBUG("%u\n", auth->magic); > > @@ -127,13 +127,13 @@ int drm_authmagic(struct drm_device *dev, void *data, > > DRM_DEBUG("%u\n", auth->magic); > > - mutex_lock(&dev->master_mutex); > + spin_lock(&dev->master_lookup_lock); > file = idr_find(&file_priv->master->magic_map, auth->magic); > if (file) { > file->authenticated = 1; > idr_replace(&file_priv->master->magic_map, NULL, auth->magic); > } > - mutex_unlock(&dev->master_mutex); > + spin_unlock(&dev->master_lookup_lock); > > return file ? 0 : -EINVAL; > } > @@ -366,8 +366,10 @@ void drm_master_release(struct drm_file *file_priv) > if (!master) > goto unlock; > > + spin_lock(&dev->master_lookup_lock); > if (file_priv->magic) > idr_remove(&master->magic_map, file_priv->magic); > + spin_unlock(&dev->master_lookup_lock); > > if (!drm_is_current_master_locked(file_priv)) > goto out; > diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c > index 4d029d3061d9..e5c3845b6e62 100644 > --- a/drivers/gpu/drm/drm_ioctl.c > +++ b/drivers/gpu/drm/drm_ioctl.c > @@ -119,21 +119,21 @@ int drm_getunique(struct drm_device *dev, void *data, > struct drm_unique *u = data; > struct drm_master *master; > > - mutex_lock(&dev->master_mutex); > + spin_lock(&dev->master_lookup_lock); > master = file_priv->master; > if (!master) { > - mutex_unlock(&dev->master_mutex); > + spin_unlock(&dev->master_lookup_lock); > return -EINVAL; > } > > if (u->unique_len >= master->unique_len) { > if (copy_to_user(u->unique, master->unique, master->unique_len)) { > - mutex_unlock(&dev->master_mutex); > + spin_unlock(&dev->master_lookup_lock); copy_to_user while holding a spinlock isn't going to work well, at least when we take a fault. The might_fault() annotations (if enabled) should catch that. Which is really annoying, because it kinda puts a wrench into this neat plan here :-/ > return -EFAULT; > } > } > u->unique_len = master->unique_len; > - mutex_unlock(&dev->master_mutex); > + spin_unlock(&dev->master_lookup_lock); > > return 0; > } > @@ -405,7 +405,9 @@ static int drm_setversion(struct drm_device *dev, void *data, struct drm_file *f > * Version 1.1 includes tying of DRM to specific device > * Version 1.4 has proper PCI domain support > */ > + spin_lock(&dev->master_lookup_lock); > retcode = drm_set_busid(dev, file_priv); > + spin_unlock(&dev->master_lookup_lock); Similar issue with drm_set_busid, calling kmalloc under a spinlock isn't a good idea. This one here is at least much easier to fix by pushing the locking down a lot. I'm wondering a bit whether a better fix for these ioctls wouldn't be to - drop the DRM_MASTER flag from the ioctl table - take the rwsem in write mode (which would replace our current dev->master_lock) and check for master status while holding that lock I think that would result in simpler locking or am I missing something? Maybe this could even work as a replacment for the lookup spinlock, since we're untangling the nesting quite a bit? Really just tossing ideas around since I feel like we don't have the best one yet ... -Daniel > if (retcode) > goto done; > } > diff --git a/include/drm/drm_auth.h b/include/drm/drm_auth.h > index ba248ca8866f..f5be73153798 100644 > --- a/include/drm/drm_auth.h > +++ b/include/drm/drm_auth.h > @@ -67,17 +67,17 @@ struct drm_master { > struct drm_device *dev; > /** > * @unique: Unique identifier: e.g. busid. Protected by > - * &drm_device.master_mutex. > + * &drm_device.master_lookup_lock. > */ > char *unique; > /** > * @unique_len: Length of unique field. Protected by > - * &drm_device.master_mutex. > + * &drm_device.master_lookup_lock. > */ > int unique_len; > /** > * @magic_map: Map of used authentication tokens. Protected by > - * &drm_device.master_mutex. > + * &drm_device.master_lookup_lock. > */ > struct idr magic_map; > void *driver_priv; > diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h > index 506eb2784819..cf5d15aeb25f 100644 > --- a/include/drm/drm_device.h > +++ b/include/drm/drm_device.h > @@ -152,7 +152,12 @@ struct drm_device { > */ > struct mutex master_mutex; > > - /** @master_lookup_lock: Serializes &drm_file.master. */ > + /** > + * @master_lookup_lock: > + * > + * Serializes &drm_file.master, &drm_master.magic_map, > + * &drm_master.unique, and &drm_master.unique_len. > + */ > spinlock_t master_lookup_lock; > > /** > -- > 2.25.1 >
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index b7230604496b..0acb444fbbac 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -98,10 +98,10 @@ int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv) struct drm_master *master; int ret = 0; - mutex_lock(&dev->master_mutex); + spin_lock(&dev->master_lookup_lock); master = file_priv->master; if (!master) { - mutex_unlock(&dev->master_mutex); + spin_unlock(&dev->master_lookup_lock); return -EINVAL; } @@ -112,7 +112,7 @@ int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv) file_priv->magic = ret; } auth->magic = file_priv->magic; - mutex_unlock(&dev->master_mutex); + spin_unlock(&dev->master_lookup_lock); DRM_DEBUG("%u\n", auth->magic); @@ -127,13 +127,13 @@ int drm_authmagic(struct drm_device *dev, void *data, DRM_DEBUG("%u\n", auth->magic); - mutex_lock(&dev->master_mutex); + spin_lock(&dev->master_lookup_lock); file = idr_find(&file_priv->master->magic_map, auth->magic); if (file) { file->authenticated = 1; idr_replace(&file_priv->master->magic_map, NULL, auth->magic); } - mutex_unlock(&dev->master_mutex); + spin_unlock(&dev->master_lookup_lock); return file ? 0 : -EINVAL; } @@ -366,8 +366,10 @@ void drm_master_release(struct drm_file *file_priv) if (!master) goto unlock; + spin_lock(&dev->master_lookup_lock); if (file_priv->magic) idr_remove(&master->magic_map, file_priv->magic); + spin_unlock(&dev->master_lookup_lock); if (!drm_is_current_master_locked(file_priv)) goto out; diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c index 4d029d3061d9..e5c3845b6e62 100644 --- a/drivers/gpu/drm/drm_ioctl.c +++ b/drivers/gpu/drm/drm_ioctl.c @@ -119,21 +119,21 @@ int drm_getunique(struct drm_device *dev, void *data, struct drm_unique *u = data; struct drm_master *master; - mutex_lock(&dev->master_mutex); + spin_lock(&dev->master_lookup_lock); master = file_priv->master; if (!master) { - mutex_unlock(&dev->master_mutex); + spin_unlock(&dev->master_lookup_lock); return -EINVAL; } if (u->unique_len >= master->unique_len) { if (copy_to_user(u->unique, master->unique, master->unique_len)) { - mutex_unlock(&dev->master_mutex); + spin_unlock(&dev->master_lookup_lock); return -EFAULT; } } u->unique_len = master->unique_len; - mutex_unlock(&dev->master_mutex); + spin_unlock(&dev->master_lookup_lock); return 0; } @@ -405,7 +405,9 @@ static int drm_setversion(struct drm_device *dev, void *data, struct drm_file *f * Version 1.1 includes tying of DRM to specific device * Version 1.4 has proper PCI domain support */ + spin_lock(&dev->master_lookup_lock); retcode = drm_set_busid(dev, file_priv); + spin_unlock(&dev->master_lookup_lock); if (retcode) goto done; } diff --git a/include/drm/drm_auth.h b/include/drm/drm_auth.h index ba248ca8866f..f5be73153798 100644 --- a/include/drm/drm_auth.h +++ b/include/drm/drm_auth.h @@ -67,17 +67,17 @@ struct drm_master { struct drm_device *dev; /** * @unique: Unique identifier: e.g. busid. Protected by - * &drm_device.master_mutex. + * &drm_device.master_lookup_lock. */ char *unique; /** * @unique_len: Length of unique field. Protected by - * &drm_device.master_mutex. + * &drm_device.master_lookup_lock. */ int unique_len; /** * @magic_map: Map of used authentication tokens. Protected by - * &drm_device.master_mutex. + * &drm_device.master_lookup_lock. */ struct idr magic_map; void *driver_priv; diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h index 506eb2784819..cf5d15aeb25f 100644 --- a/include/drm/drm_device.h +++ b/include/drm/drm_device.h @@ -152,7 +152,12 @@ struct drm_device { */ struct mutex master_mutex; - /** @master_lookup_lock: Serializes &drm_file.master. */ + /** + * @master_lookup_lock: + * + * Serializes &drm_file.master, &drm_master.magic_map, + * &drm_master.unique, and &drm_master.unique_len. + */ spinlock_t master_lookup_lock; /**
Currently, drm_device.master_mutex is used to serialize writes to the drm_master.magic_map idr and to protect drm_master.unique{_len}. In preparation for converting drm_device.master_mutex into an outer rwsem that might be read locked before entering some of these functions, we can instead serialize access to drm_master.magic_map and drm_master.unique{_len} using drm_device.master_lookup_lock which is an inner lock. Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> --- drivers/gpu/drm/drm_auth.c | 12 +++++++----- drivers/gpu/drm/drm_ioctl.c | 10 ++++++---- include/drm/drm_auth.h | 6 +++--- include/drm/drm_device.h | 7 ++++++- 4 files changed, 22 insertions(+), 13 deletions(-)