[PATCH v2] drm: make DRM_UNLOCKED ioctls with their own mutex

[Ilija Hadzic]

drm_getclient, drm_getstats and drm_getmap (with a few minor
adjustments) do not need global mutex, so fix that and
make the said ioctls DRM_UNLOCKED. Details:

  drm_getclient: the only thing that should be protected here
  is dev->filelist and that is already protected everywhere with
  dev->struct_mutex.

  drm_getstats: there is no need for any mutex here because the
  loop runs through quasi-static (set at load time only)
  data, and the actual count access is done with atomic_read()

  drm_getmap already uses dev->struct_mutex to protect
  dev->maplist, which also used to protect the same structure
  everywhere else except at three places:
  * drm_getsarea, which doesn't grab *any* mutex before
    touching dev->maplist (so no drm_global_mutex doesn't help
    here either; different issue for a different patch).
    However, drivers seem to call it only at
    initialization time so it probably doesn't matter
  * drm_master_destroy, which is called from drm_master_put,
    which in turn is protected with dev->struct_mutex
    everywhere else in drm module, so we are good here too.
  * drm_getsareactx, which releases the dev->struct_mutex
    too early, but this patch includes the fix for that.

v2: * incorporate comments received from Daniel Vetter
    * include the (long) explanation above to make it clear what
      we are doing (and why), also at Daniel Vetter's request
    * tighten up mutex grab/release locations to only
      encompass real critical sections, rather than some
      random code around them

Signed-off-by: Ilija Hadzic <ihadzic at research.bell-labs.com>
---
 drivers/gpu/drm/drm_context.c |    5 +++--
 drivers/gpu/drm/drm_drv.c     |    6 +++---
 drivers/gpu/drm/drm_ioctl.c   |   15 ++++-----------
 3 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/drm_context.c b/drivers/gpu/drm/drm_context.c
index 6d440fb..325365f 100644
--- a/drivers/gpu/drm/drm_context.c
+++ b/drivers/gpu/drm/drm_context.c
@@ -154,8 +154,6 @@ int drm_getsareactx(struct drm_device *dev, void *data,
 		return -EINVAL;
 	}
 
-	mutex_unlock(&dev->struct_mutex);
-
 	request->handle = NULL;
 	list_for_each_entry(_entry, &dev->maplist, head) {
 		if (_entry->map == map) {
@@ -164,6 +162,9 @@ int drm_getsareactx(struct drm_device *dev, void *data,
 			break;
 		}
 	}
+
+	mutex_unlock(&dev->struct_mutex);
+
 	if (request->handle == NULL)
 		return -EINVAL;
 
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index c990dab..dc0eb0b 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -64,9 +64,9 @@ static struct drm_ioctl_desc drm_ioctls[] = {
 	DRM_IOCTL_DEF(DRM_IOCTL_GET_UNIQUE, drm_getunique, 0),
 	DRM_IOCTL_DEF(DRM_IOCTL_GET_MAGIC, drm_getmagic, 0),
 	DRM_IOCTL_DEF(DRM_IOCTL_IRQ_BUSID, drm_irq_by_busid, DRM_MASTER|DRM_ROOT_ONLY),
-	DRM_IOCTL_DEF(DRM_IOCTL_GET_MAP, drm_getmap, 0),
-	DRM_IOCTL_DEF(DRM_IOCTL_GET_CLIENT, drm_getclient, 0),
-	DRM_IOCTL_DEF(DRM_IOCTL_GET_STATS, drm_getstats, 0),
+	DRM_IOCTL_DEF(DRM_IOCTL_GET_MAP, drm_getmap, DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_IOCTL_GET_CLIENT, drm_getclient, DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_IOCTL_GET_STATS, drm_getstats, DRM_UNLOCKED),
 	DRM_IOCTL_DEF(DRM_IOCTL_GET_CAP, drm_getcap, DRM_UNLOCKED),
 	DRM_IOCTL_DEF(DRM_IOCTL_SET_VERSION, drm_setversion, DRM_MASTER),
 
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 904d7e9..956fd38 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -158,14 +158,11 @@ int drm_getmap(struct drm_device *dev, void *data,
 	int i;
 
 	idx = map->offset;
-
-	mutex_lock(&dev->struct_mutex);
-	if (idx < 0) {
-		mutex_unlock(&dev->struct_mutex);
+	if (idx < 0)
 		return -EINVAL;
-	}
 
 	i = 0;
+	mutex_lock(&dev->struct_mutex);
 	list_for_each(list, &dev->maplist) {
 		if (i == idx) {
 			r_list = list_entry(list, struct drm_map_list, head);
@@ -211,9 +208,9 @@ int drm_getclient(struct drm_device *dev, void *data,
 	int i;
 
 	idx = client->idx;
-	mutex_lock(&dev->struct_mutex);
-
 	i = 0;
+
+	mutex_lock(&dev->struct_mutex);
 	list_for_each_entry(pt, &dev->filelist, lhead) {
 		if (i++ >= idx) {
 			client->auth = pt->authenticated;
@@ -249,8 +246,6 @@ int drm_getstats(struct drm_device *dev, void *data,
 
 	memset(stats, 0, sizeof(*stats));
 
-	mutex_lock(&dev->struct_mutex);
-
 	for (i = 0; i < dev->counters; i++) {
 		if (dev->types[i] == _DRM_STAT_LOCK)
 			stats->data[i].value =
@@ -262,8 +257,6 @@ int drm_getstats(struct drm_device *dev, void *data,
 
 	stats->count = dev->counters;
 
-	mutex_unlock(&dev->struct_mutex);
-
 	return 0;
 }
 
-- 
1.7.7