Hi
On Tue, Mar 25, 2014 at 2:18 PM, Thomas Hellstrom <thellstrom@xxxxxxxxxx> wrote:
> The master management was previously protected by the drm_device::struct_mutex.
> In order to avoid locking order violations in a reworked dropped master
> security check in the vmwgfx driver, break it out into a separate master_mutex.
Could you elaborate on that? What exactly is "master_mutex"
protecting? "struct_mutex" is used to serialize all entry-points into
the drm-device (and thus the driver) and also, often implicitly, as
spin-lock for "struct drm_device" data protection.
Regarding master_mutex I have several questions:
- Can you give an example how vmwgfx dead-locks with your reworked code?
- Why don't add a spin-lock to "drm_file" instead? Use that one to
manage master contexts, but keep "struct_mutex" whenever calling into
driver callbacks (set_master/drop_master)
- why is master_mutex per device and not per-minor? I thought masters
on minors are _entirely_ independent?
Few more comments inline.
> Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
> Reviewed-by: Brian Paul <brianp@xxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_fops.c | 23 +++++++++++++---------
> drivers/gpu/drm/drm_stub.c | 38 ++++++++++++++++++++++--------------
> include/drm/drmP.h | 46 ++++++++++++++++++++++++--------------------
> 3 files changed, 63 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
> index e6cdd0f..dad571f 100644
> --- a/drivers/gpu/drm/drm_fops.c
> +++ b/drivers/gpu/drm/drm_fops.c
> @@ -231,12 +231,13 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
>
> /* if there is no current master make this fd it, but do not create
> * any master object for render clients */
> - mutex_lock(&dev->struct_mutex);
> + mutex_lock(&dev->master_mutex);
> if (drm_is_legacy_client(priv) && !priv->minor->master) {
> /* create a new master */
> + mutex_lock(&dev->struct_mutex);
> priv->minor->master = drm_master_create(priv->minor);
> + mutex_unlock(&dev->struct_mutex);
> if (!priv->minor->master) {
> - mutex_unlock(&dev->struct_mutex);
> ret = -ENOMEM;
> goto out_close;
> }
> @@ -245,28 +246,25 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
> /* take another reference for the copy in the local file priv */
> priv->master = drm_master_get(priv->minor->master);
>
> + mutex_lock(&dev->struct_mutex);
> priv->authenticated = 1;
>
> mutex_unlock(&dev->struct_mutex);
What's that struct_mutex doing here? We're in ->open(), there is
no-one racing against us.
> if (dev->driver->master_create) {
> ret = dev->driver->master_create(dev, priv->master);
> if (ret) {
> - mutex_lock(&dev->struct_mutex);
> /* drop both references if this fails */
> drm_master_put(&priv->minor->master);
> drm_master_put(&priv->master);
> - mutex_unlock(&dev->struct_mutex);
> goto out_close;
> }
> }
> - mutex_lock(&dev->struct_mutex);
> if (dev->driver->master_set) {
> ret = dev->driver->master_set(dev, priv, true);
> if (ret) {
> /* drop both references if this fails */
> drm_master_put(&priv->minor->master);
> drm_master_put(&priv->master);
> - mutex_unlock(&dev->struct_mutex);
> goto out_close;
> }
> }
> @@ -274,8 +272,8 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
> /* get a reference to the master */
> priv->master = drm_master_get(priv->minor->master);
> }
> - mutex_unlock(&dev->struct_mutex);
>
> + mutex_unlock(&dev->master_mutex);
> mutex_lock(&dev->struct_mutex);
> list_add(&priv->lhead, &dev->filelist);
> mutex_unlock(&dev->struct_mutex);
> @@ -302,6 +300,7 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
> return 0;
>
> out_close:
> + mutex_unlock(&dev->master_mutex);
> if (dev->driver->postclose)
> dev->driver->postclose(dev, priv);
> out_prime_destroy:
> @@ -489,11 +488,13 @@ int drm_release(struct inode *inode, struct file *filp)
> }
> mutex_unlock(&dev->ctxlist_mutex);
>
> - mutex_lock(&dev->struct_mutex);
> + mutex_lock(&dev->master_mutex);
>
> if (file_priv->is_master) {
> struct drm_master *master = file_priv->master;
> struct drm_file *temp;
> +
> + mutex_lock(&dev->struct_mutex);
> list_for_each_entry(temp, &dev->filelist, lhead) {
> if ((temp->master == file_priv->master) &&
> (temp != file_priv))
> @@ -512,6 +513,7 @@ int drm_release(struct inode *inode, struct file *filp)
> master->lock.file_priv = NULL;
> wake_up_interruptible_all(&master->lock.lock_queue);
> }
> + mutex_unlock(&dev->struct_mutex);
>
> if (file_priv->minor->master == file_priv->master) {
> /* drop the reference held my the minor */
> @@ -521,10 +523,13 @@ int drm_release(struct inode *inode, struct file *filp)
> }
> }
>
> - /* drop the reference held my the file priv */
> + /* drop the master reference held by the file priv */
> if (file_priv->master)
> drm_master_put(&file_priv->master);
> file_priv->is_master = 0;
> + mutex_unlock(&dev->master_mutex);
> +
> + mutex_lock(&dev->struct_mutex);
> list_del(&file_priv->lhead);
> mutex_unlock(&dev->struct_mutex);
>
> diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c
> index d344513..10c8303 100644
> --- a/drivers/gpu/drm/drm_stub.c
> +++ b/drivers/gpu/drm/drm_stub.c
> @@ -152,6 +152,7 @@ static void drm_master_destroy(struct kref *kref)
> struct drm_device *dev = master->minor->dev;
> struct drm_map_list *r_list, *list_temp;
>
> + mutex_lock(&dev->struct_mutex);
> if (dev->driver->master_destroy)
> dev->driver->master_destroy(dev, master);
>
> @@ -179,6 +180,7 @@ static void drm_master_destroy(struct kref *kref)
>
> drm_ht_remove(&master->magiclist);
>
> + mutex_unlock(&dev->struct_mutex);
> kfree(master);
> }
>
> @@ -194,19 +196,17 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
> {
> int ret = 0;
>
> + mutex_lock(&dev->master_mutex);
> if (file_priv->is_master)
> - return 0;
> + goto out_unlock;
>
> - if (file_priv->minor->master && file_priv->minor->master != file_priv->master)
> - return -EINVAL;
> + ret = -EINVAL;
> + if (file_priv->minor->master)
> + goto out_unlock;
>
> if (!file_priv->master)
> - return -EINVAL;
> + goto out_unlock;
>
> - if (file_priv->minor->master)
> - return -EINVAL;
> -
> - mutex_lock(&dev->struct_mutex);
> file_priv->minor->master = drm_master_get(file_priv->master);
> file_priv->is_master = 1;
> if (dev->driver->master_set) {
> @@ -216,27 +216,33 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
> drm_master_put(&file_priv->minor->master);
> }
> }
> - mutex_unlock(&dev->struct_mutex);
>
> +out_unlock:
> + mutex_unlock(&dev->master_mutex);
> return ret;
> }
>
> int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_priv)
> {
> + int ret = -EINVAL;
> +
> + mutex_lock(&dev->master_mutex);
> if (!file_priv->is_master)
> - return -EINVAL;
> + goto out_unlock;
>
> if (!file_priv->minor->master)
> - return -EINVAL;
> + goto out_unlock;
>
> - mutex_lock(&dev->struct_mutex);
> + ret = 0;
> if (dev->driver->master_drop)
> dev->driver->master_drop(dev, file_priv, false);
> drm_master_put(&file_priv->minor->master);
> file_priv->is_master = 0;
> - mutex_unlock(&dev->struct_mutex);
> - return 0;
> +
> +out_unlock:
> + mutex_unlock(&dev->master_mutex);
> + return ret;
> }
>
> /*
> @@ -567,6 +573,7 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
> spin_lock_init(&dev->event_lock);
> mutex_init(&dev->struct_mutex);
> mutex_init(&dev->ctxlist_mutex);
> + mutex_init(&dev->master_mutex);
>
> dev->anon_inode = drm_fs_inode_new();
> if (IS_ERR(dev->anon_inode)) {
> @@ -620,6 +627,7 @@ err_minors:
> drm_minor_free(dev, DRM_MINOR_CONTROL);
> drm_fs_inode_free(dev->anon_inode);
> err_free:
> + mutex_destroy(&dev->master_mutex);
> kfree(dev);
> return NULL;
> }
> @@ -641,6 +649,8 @@ static void drm_dev_release(struct kref *ref)
> drm_minor_free(dev, DRM_MINOR_CONTROL);
>
> kfree(dev->devname);
> +
> + mutex_destroy(&dev->master_mutex);
> kfree(dev);
> }
>
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index 1521036..2b387b0 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -435,7 +435,8 @@ struct drm_prime_file_private {
> struct drm_file {
> unsigned always_authenticated :1;
> unsigned authenticated :1;
> - unsigned is_master :1; /* this file private is a master for a minor */
> + /* Whether we're master for a minor. Protected by master_mutex */
> + unsigned is_master :1;
> /* true when the client has asked us to expose stereo 3D mode flags */
> unsigned stereo_allowed :1;
>
> @@ -714,28 +715,29 @@ struct drm_gem_object {
>
> #include <drm/drm_crtc.h>
>
> -/* per-master structure */
> +/**
> + * struct drm_master - drm master structure
> + *
> + * @refcount: Refcount for this master object.
> + * @minor: Link back to minor char device we are master for. Immutable.
> + * @unique: Unique identifier: e.g. busid. Protected by drm_global_mutex.
> + * @unique_len: Length of unique field. Protected by drm_global_mutex.
> + * @unique_size: Amount allocated. Protected by drm_global_mutex.
> + * @magiclist: Hash of used authentication tokens. Protected by struct_mutex.
> + * @magicfree: List of used authentication tokens. Protected by struct_mutex.
> + * @lock: DRI lock information.
> + * @driver_priv: Pointer to driver-private information.
> + */
> struct drm_master {
> -
> - struct kref refcount; /* refcount for this master */
> -
> - struct drm_minor *minor; /**< link back to minor we are a master for */
> -
> - char *unique; /**< Unique identifier: e.g., busid */
> - int unique_len; /**< Length of unique field */
> - int unique_size; /**< amount allocated */
> -
> - int blocked; /**< Blocked due to VC switch? */
You silently dropped that field. At least mention it in the
commit-message if it's unused.
> -
> - /** \name Authentication */
> - /*@{ */
> + struct kref refcount;
> + struct drm_minor *minor;
> + char *unique;
> + int unique_len;
> + int unique_size;
> struct drm_open_hash magiclist;
> struct list_head magicfree;
> - /*@} */
> -
> - struct drm_lock_data lock; /**< Information on hardware lock */
> -
> - void *driver_priv; /**< Private structure for driver to use */
> + struct drm_lock_data lock;
> + void *driver_priv;
> };
>
> /* Size of ringbuffer for vblank timestamps. Just double-buffer
> @@ -1050,7 +1052,8 @@ struct drm_minor {
> struct list_head debugfs_list;
> struct mutex debugfs_lock; /* Protects debugfs_list. */
>
> - struct drm_master *master; /* currently active master for this node */
> + /* currently active master for this node. Protected by master_mutex */
> + struct drm_master *master;
> struct drm_mode_group mode_group;
> };
>
> @@ -1100,6 +1103,7 @@ struct drm_device {
> /*@{ */
> spinlock_t count_lock; /**< For inuse, drm_device::open_count, drm_device::buf_use */
> struct mutex struct_mutex; /**< For others */
> + struct mutex master_mutex;
Comments, comments, comments! Lets avoid adding another undocumented
mutex here. Or at least mark it as private to drm_master_*()
functions.
Thanks
David
> /*@} */
>
> /** \name Usage Counters */
> --
> 1.7.10.4
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