From 9b2c0b7fb4ce79566d830d03ce7aa11cccc39f97 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Wed, 25 Nov 2015 14:39:03 +0000 Subject: [PATCH] drm: Serialise multiple event readers The previous patch reintroduced a race condition whereby a failure in one reader may allow a second reader to see out-of-order events. Introduce a mutex to serialise readers so that an event is completed in its entirety before another reader may process an event. The two readers may race against each other, but the events each retrieves are in the correct order. Signed-off-by: Chris Wilson Cc: Thomas Hellstrom Cc: Takashi Iwai Cc: Daniel Vetter Link: http://patchwork.freedesktop.org/patch/msgid/1448462343-2072-2-git-send-email-chris@chris-wilson.co.uk Reviewed-by: Thomas Hellstrom Signed-off-by: Daniel Vetter --- drivers/gpu/drm/drm_fops.c | 18 +++++++++++++----- include/drm/drmP.h | 2 ++ 2 files changed, 15 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c index eb8702d..81df9ae 100644 --- a/drivers/gpu/drm/drm_fops.c +++ b/drivers/gpu/drm/drm_fops.c @@ -172,6 +172,8 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor) init_waitqueue_head(&priv->event_wait); priv->event_space = 4096; /* set aside 4k for event buffer */ + mutex_init(&priv->event_read_lock); + if (drm_core_check_feature(dev, DRIVER_GEM)) drm_gem_open(dev, priv); @@ -483,11 +485,15 @@ ssize_t drm_read(struct file *filp, char __user *buffer, { struct drm_file *file_priv = filp->private_data; struct drm_device *dev = file_priv->minor->dev; - ssize_t ret = 0; + ssize_t ret; if (!access_ok(VERIFY_WRITE, buffer, count)) return -EFAULT; + ret = mutex_lock_interruptible(&file_priv->event_read_lock); + if (ret) + return ret; + for (;;) { struct drm_pending_event *e = NULL; @@ -509,12 +515,13 @@ ssize_t drm_read(struct file *filp, char __user *buffer, break; } + mutex_unlock(&file_priv->event_read_lock); ret = wait_event_interruptible(file_priv->event_wait, !list_empty(&file_priv->event_list)); - if (ret < 0) - break; - - ret = 0; + if (ret >= 0) + ret = mutex_lock_interruptible(&file_priv->event_read_lock); + if (ret) + return ret; } else { unsigned length = e->event->length; @@ -537,6 +544,7 @@ put_back_event: e->destroy(e); } } + mutex_unlock(&file_priv->event_read_lock); return ret; } diff --git a/include/drm/drmP.h b/include/drm/drmP.h index 30d4a5a..8e1df1f 100644 --- a/include/drm/drmP.h +++ b/include/drm/drmP.h @@ -344,6 +344,8 @@ struct drm_file { struct list_head event_list; int event_space; + struct mutex event_read_lock; + struct drm_prime_file_private prime; }; -- 2.7.4