The current implementation of drm_read() faces a number of issues:
1. Upon an error, it consumes the event which may lead to the client blocking. 2. Upon an error, it forgets about events already copied 3. If it fails to copy a single event with O_NONBLOCK it falls into a infinite loop of reporting EAGAIN. 3. There is a race between multiple waiters and blocking reads of the events list.
Here, we inline drm_dequeue_event() into drm_read() so that we can take the spinlock around the list walking and event copying, and importantly reorder the error handling to avoid the issues above.
Cc: Takashi Iwai tiwai@suse.de Signed-off-by: Chris Wilson chris@chris-wilson.co.uk --- drivers/gpu/drm/drm_fops.c | 90 ++++++++++++++++++++++------------------------ 1 file changed, 43 insertions(+), 47 deletions(-)
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c index 91e1105f2800..076dd606b580 100644 --- a/drivers/gpu/drm/drm_fops.c +++ b/drivers/gpu/drm/drm_fops.c @@ -478,63 +478,59 @@ int drm_release(struct inode *inode, struct file *filp) } EXPORT_SYMBOL(drm_release);
-static bool -drm_dequeue_event(struct drm_file *file_priv, - size_t total, size_t max, struct drm_pending_event **out) +ssize_t drm_read(struct file *filp, char __user *buffer, + size_t count, loff_t *offset) { + struct drm_file *file_priv = filp->private_data; struct drm_device *dev = file_priv->minor->dev; - struct drm_pending_event *e; - unsigned long flags; - bool ret = false; - - spin_lock_irqsave(&dev->event_lock, flags); + ssize_t ret = 0;
- *out = NULL; - if (list_empty(&file_priv->event_list)) - goto out; - e = list_first_entry(&file_priv->event_list, - struct drm_pending_event, link); - if (e->event->length + total > max) - goto out; + if (!access_ok(VERIFY_WRITE, buffer, count)) + return -EFAULT;
- file_priv->event_space += e->event->length; - list_del(&e->link); - *out = e; - ret = true; + spin_lock_irq(&dev->event_lock); + for (;;) { + if (list_empty(&file_priv->event_list)) { + if (ret) + break;
-out: - spin_unlock_irqrestore(&dev->event_lock, flags); - return ret; -} - -ssize_t drm_read(struct file *filp, char __user *buffer, - size_t count, loff_t *offset) -{ - struct drm_file *file_priv = filp->private_data; - struct drm_pending_event *e; - size_t total; - ssize_t ret; + if (filp->f_flags & O_NONBLOCK) { + ret = -EAGAIN; + break; + }
- if ((filp->f_flags & O_NONBLOCK) == 0) { - ret = wait_event_interruptible(file_priv->event_wait, - !list_empty(&file_priv->event_list)); - if (ret < 0) - return ret; - } + spin_unlock_irq(&dev->event_lock); + ret = wait_event_interruptible(file_priv->event_wait, + !list_empty(&file_priv->event_list)); + spin_lock_irq(&dev->event_lock); + if (ret < 0) + break; + + ret = 0; + } else { + struct drm_pending_event *e; + + e = list_first_entry(&file_priv->event_list, + struct drm_pending_event, link); + if (e->event->length + ret > count) + break; + + if (__copy_to_user_inatomic(buffer + ret, + e->event, e->event->length)) { + if (ret == 0) + ret = -EFAULT; + break; + }
- total = 0; - while (drm_dequeue_event(file_priv, total, count, &e)) { - if (copy_to_user(buffer + total, - e->event, e->event->length)) { - total = -EFAULT; - break; + file_priv->event_space += e->event->length; + ret += e->event->length; + list_del(&e->link); + e->destroy(e); } - - total += e->event->length; - e->destroy(e); } + spin_unlock_irq(&dev->event_lock);
- return total ?: -EAGAIN; + return ret; } EXPORT_SYMBOL(drm_read);