[PATCH v2] drm/fb-helper: Avoid race with DRM userspace
Noralf Trønnes
noralf at tronnes.org
Fri Apr 26 13:10:27 UTC 2019
drm_fb_helper_is_bound() is used to check if DRM userspace is in control.
This is done by looking at the fb on the primary plane. By the time
fb-helper gets around to committing, it's possible that the facts have
changed.
Avoid this race by holding the drm_device->master_mutex lock while
committing. When DRM userspace does its first open, it will now wait
until fb-helper is done. The helper will stay away if there's a master.
Locking rule: Always take the fb-helper lock first.
v2:
- Remove drm_fb_helper_is_bound() (Daniel Vetter)
- No need to check fb_helper->dev->master in
drm_fb_helper_single_fb_probe(), restore_fbdev_mode() has the check.
Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
drivers/gpu/drm/drm_auth.c | 20 ++++++++++++
drivers/gpu/drm/drm_fb_helper.c | 57 ++++++++++++++++++++++++---------
drivers/gpu/drm/drm_internal.h | 2 ++
3 files changed, 63 insertions(+), 16 deletions(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index 1669c42c40ed..db199807b7dc 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -368,3 +368,23 @@ void drm_master_put(struct drm_master **master)
*master = NULL;
}
EXPORT_SYMBOL(drm_master_put);
+
+/* Used by drm_client and drm_fb_helper */
+bool drm_master_internal_acquire(struct drm_device *dev)
+{
+ mutex_lock(&dev->master_mutex);
+ if (dev->master) {
+ mutex_unlock(&dev->master_mutex);
+ return false;
+ }
+
+ return true;
+}
+EXPORT_SYMBOL(drm_master_internal_acquire);
+
+/* Used by drm_client and drm_fb_helper */
+void drm_master_internal_release(struct drm_device *dev)
+{
+ mutex_unlock(&dev->master_mutex);
+}
+EXPORT_SYMBOL(drm_master_internal_release);
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 2339f0f8f5a8..25d28deb9210 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -44,6 +44,7 @@
#include "drm_crtc_internal.h"
#include "drm_crtc_helper_internal.h"
+#include "drm_internal.h"
static bool drm_fbdev_emulation = true;
module_param_named(fbdev_emulation, drm_fbdev_emulation, bool, 0600);
@@ -509,7 +510,7 @@ static int restore_fbdev_mode_legacy(struct drm_fb_helper *fb_helper)
return ret;
}
-static int restore_fbdev_mode(struct drm_fb_helper *fb_helper)
+static int restore_fbdev_mode_force(struct drm_fb_helper *fb_helper)
{
struct drm_device *dev = fb_helper->dev;
@@ -519,6 +520,21 @@ static int restore_fbdev_mode(struct drm_fb_helper *fb_helper)
return restore_fbdev_mode_legacy(fb_helper);
}
+static int restore_fbdev_mode(struct drm_fb_helper *fb_helper)
+{
+ struct drm_device *dev = fb_helper->dev;
+ int ret;
+
+ if (!drm_master_internal_acquire(dev))
+ return -EBUSY;
+
+ ret = restore_fbdev_mode_force(fb_helper);
+
+ drm_master_internal_release(dev);
+
+ return ret;
+}
+
/**
* drm_fb_helper_restore_fbdev_mode_unlocked - restore fbdev configuration
* @fb_helper: driver-allocated fbdev helper, can be NULL
@@ -604,7 +620,7 @@ static bool drm_fb_helper_force_kernel_mode(void)
continue;
mutex_lock(&helper->lock);
- ret = restore_fbdev_mode(helper);
+ ret = restore_fbdev_mode_force(helper);
if (ret)
error = true;
mutex_unlock(&helper->lock);
@@ -663,20 +679,22 @@ static void dpms_legacy(struct drm_fb_helper *fb_helper, int dpms_mode)
static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
{
struct drm_fb_helper *fb_helper = info->par;
+ struct drm_device *dev = fb_helper->dev;
/*
* For each CRTC in this fb, turn the connectors on/off.
*/
mutex_lock(&fb_helper->lock);
- if (!drm_fb_helper_is_bound(fb_helper)) {
- mutex_unlock(&fb_helper->lock);
- return;
- }
+ if (!drm_master_internal_acquire(dev))
+ goto unlock;
- if (drm_drv_uses_atomic_modeset(fb_helper->dev))
+ if (drm_drv_uses_atomic_modeset(dev))
restore_fbdev_mode_atomic(fb_helper, dpms_mode == DRM_MODE_DPMS_ON);
else
dpms_legacy(fb_helper, dpms_mode);
+
+ drm_master_internal_release(dev);
+unlock:
mutex_unlock(&fb_helper->lock);
}
@@ -1509,6 +1527,7 @@ static int setcmap_atomic(struct fb_cmap *cmap, struct fb_info *info)
int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
{
struct drm_fb_helper *fb_helper = info->par;
+ struct drm_device *dev = fb_helper->dev;
int ret;
if (oops_in_progress)
@@ -1516,9 +1535,9 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
mutex_lock(&fb_helper->lock);
- if (!drm_fb_helper_is_bound(fb_helper)) {
+ if (!drm_master_internal_acquire(dev)) {
ret = -EBUSY;
- goto out;
+ goto unlock;
}
if (info->fix.visual == FB_VISUAL_TRUECOLOR)
@@ -1528,7 +1547,8 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
else
ret = setcmap_legacy(cmap, info);
-out:
+ drm_master_internal_release(dev);
+unlock:
mutex_unlock(&fb_helper->lock);
return ret;
@@ -1548,12 +1568,13 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
unsigned long arg)
{
struct drm_fb_helper *fb_helper = info->par;
+ struct drm_device *dev = fb_helper->dev;
struct drm_mode_set *mode_set;
struct drm_crtc *crtc;
int ret = 0;
mutex_lock(&fb_helper->lock);
- if (!drm_fb_helper_is_bound(fb_helper)) {
+ if (!drm_master_internal_acquire(dev)) {
ret = -EBUSY;
goto unlock;
}
@@ -1591,11 +1612,12 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
}
ret = 0;
- goto unlock;
+ break;
default:
ret = -ENOTTY;
}
+ drm_master_internal_release(dev);
unlock:
mutex_unlock(&fb_helper->lock);
return ret;
@@ -1847,15 +1869,18 @@ int drm_fb_helper_pan_display(struct fb_var_screeninfo *var,
return -EBUSY;
mutex_lock(&fb_helper->lock);
- if (!drm_fb_helper_is_bound(fb_helper)) {
- mutex_unlock(&fb_helper->lock);
- return -EBUSY;
+ if (!drm_master_internal_acquire(dev)) {
+ ret = -EBUSY;
+ goto unlock;
}
if (drm_drv_uses_atomic_modeset(dev))
ret = pan_display_atomic(var, info);
else
ret = pan_display_legacy(var, info);
+
+ drm_master_internal_release(dev);
+unlock:
mutex_unlock(&fb_helper->lock);
return ret;
@@ -2014,7 +2039,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
DRM_INFO("Cannot find any crtc or sizes\n");
/* First time: disable all crtc's.. */
- if (!fb_helper->deferred_setup && !READ_ONCE(fb_helper->dev->master))
+ if (!fb_helper->deferred_setup)
restore_fbdev_mode(fb_helper);
return -EAGAIN;
}
diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
index d9a483a5fce0..3ee97c9998a2 100644
--- a/drivers/gpu/drm/drm_internal.h
+++ b/drivers/gpu/drm/drm_internal.h
@@ -91,6 +91,8 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
struct drm_file *file_priv);
int drm_master_open(struct drm_file *file_priv);
void drm_master_release(struct drm_file *file_priv);
+bool drm_master_internal_acquire(struct drm_device *dev);
+void drm_master_internal_release(struct drm_device *dev);
/* drm_sysfs.c */
extern struct class *drm_class;
--
2.20.1
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