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drm: Serialise multiple event readers

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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 <chris@chris-wilson.co.uk>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1448462343-2072-2-git-send-email-chris@chris-wilson.co.uk
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Chris Wilson 2015-11-25 14:39:03 +00:00 committed by Daniel Vetter
parent 83eb64c85b
commit 9b2c0b7fb4
2 changed files with 15 additions and 5 deletions
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18
drivers/gpu/drm/drm_fops.c
View File

@ -172,6 +172,8 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor)
init_waitqueue_head(&priv->event_wait); init_waitqueue_head(&priv->event_wait);
priv->event_space = 4096; /* set aside 4k for event buffer */ priv->event_space = 4096; /* set aside 4k for event buffer */
mutex_init(&priv->event_read_lock);
if (drm_core_check_feature(dev, DRIVER_GEM)) if (drm_core_check_feature(dev, DRIVER_GEM))
drm_gem_open(dev, priv); 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_file *file_priv = filp->private_data;
struct drm_device *dev = file_priv->minor->dev; struct drm_device *dev = file_priv->minor->dev;
ssize_t ret = 0; ssize_t ret;
if (!access_ok(VERIFY_WRITE, buffer, count)) if (!access_ok(VERIFY_WRITE, buffer, count))
return -EFAULT; return -EFAULT;
ret = mutex_lock_interruptible(&file_priv->event_read_lock);
if (ret)
return ret;
for (;;) { for (;;) {
struct drm_pending_event *e = NULL; struct drm_pending_event *e = NULL;
@ -509,12 +515,13 @@ ssize_t drm_read(struct file *filp, char __user *buffer,
break; break;
} }
mutex_unlock(&file_priv->event_read_lock);
ret = wait_event_interruptible(file_priv->event_wait, ret = wait_event_interruptible(file_priv->event_wait,
!list_empty(&file_priv->event_list)); !list_empty(&file_priv->event_list));
if (ret < 0) if (ret >= 0)
break; ret = mutex_lock_interruptible(&file_priv->event_read_lock);
if (ret)
ret = 0; return ret;
} else { } else {
unsigned length = e->event->length; unsigned length = e->event->length;
@ -537,6 +544,7 @@ put_back_event:
e->destroy(e); e->destroy(e);
} }
} }
mutex_unlock(&file_priv->event_read_lock);
return ret; return ret;
} }

2
include/drm/drmP.h
View File

@ -344,6 +344,8 @@ struct drm_file {
struct list_head event_list; struct list_head event_list;
int event_space; int event_space;
struct mutex event_read_lock;
struct drm_prime_file_private prime; struct drm_prime_file_private prime;
}; };