[PATCH v7 6/7] drm: avoid circular locks with modeset_mutex and master_rwsem
Desmond Cheong Zhi Xi
desmondcheongzx at gmail.com
Wed Aug 25 14:22:04 UTC 2021
drm_lease_held calls drm_file_get_master. However, this function is
sometimes called while holding on to modeset_mutex. Since
drm_device.master_rwsem will replace drm_file.master_lookup_lock in
drm_file_get_master in a future patch, this inverts the master_rwsem
--> modeset_mutex lock hierarchy.
To fix this, we create a new drm_lease_held_master helper function
that enables us to avoid calling drm_file_get_master after locking
modeset_mutex.
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx at gmail.com>
---
drivers/gpu/drm/drm_auth.c | 3 +++
drivers/gpu/drm/drm_encoder.c | 7 ++++++-
drivers/gpu/drm/drm_lease.c | 30 +++++++++++++++---------------
drivers/gpu/drm/drm_plane.c | 14 +++++++++++---
include/drm/drm_lease.h | 2 ++
5 files changed, 37 insertions(+), 19 deletions(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index 65065f7e1499..f2b2f197052a 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -410,6 +410,9 @@ struct drm_master *drm_file_get_master(struct drm_file *file_priv)
{
struct drm_master *master = NULL;
+ if (!file_priv)
+ return NULL;
+
spin_lock(&file_priv->master_lookup_lock);
if (!file_priv->master)
goto unlock;
diff --git a/drivers/gpu/drm/drm_encoder.c b/drivers/gpu/drm/drm_encoder.c
index 72e982323a5e..bacb2f6a325c 100644
--- a/drivers/gpu/drm/drm_encoder.c
+++ b/drivers/gpu/drm/drm_encoder.c
@@ -22,6 +22,7 @@
#include <linux/export.h>
+#include <drm/drm_auth.h>
#include <drm/drm_bridge.h>
#include <drm/drm_device.h>
#include <drm/drm_drv.h>
@@ -281,6 +282,7 @@ int drm_mode_getencoder(struct drm_device *dev, void *data,
struct drm_mode_get_encoder *enc_resp = data;
struct drm_encoder *encoder;
struct drm_crtc *crtc;
+ struct drm_master *master;
if (!drm_core_check_feature(dev, DRIVER_MODESET))
return -EOPNOTSUPP;
@@ -289,13 +291,16 @@ int drm_mode_getencoder(struct drm_device *dev, void *data,
if (!encoder)
return -ENOENT;
+ master = drm_file_get_master(file_priv);
drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
crtc = drm_encoder_get_crtc(encoder);
- if (crtc && drm_lease_held(file_priv, crtc->base.id))
+ if (crtc && drm_lease_held_master(master, crtc->base.id))
enc_resp->crtc_id = crtc->base.id;
else
enc_resp->crtc_id = 0;
drm_modeset_unlock(&dev->mode_config.connection_mutex);
+ if (master)
+ drm_master_put(&master);
enc_resp->encoder_type = encoder->encoder_type;
enc_resp->encoder_id = encoder->base.id;
diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c
index 1b156c85d1c8..15bf3a3c76d1 100644
--- a/drivers/gpu/drm/drm_lease.c
+++ b/drivers/gpu/drm/drm_lease.c
@@ -114,27 +114,30 @@ bool _drm_lease_held(struct drm_file *file_priv, int id)
return _drm_lease_held_master(file_priv->master, id);
}
-bool drm_lease_held(struct drm_file *file_priv, int id)
+bool drm_lease_held_master(struct drm_master *master, int id)
{
- struct drm_master *master;
bool ret;
- if (!file_priv)
+ if (!master || !master->lessor)
return true;
- master = drm_file_get_master(file_priv);
- if (!master)
- return true;
- if (!master->lessor) {
- ret = true;
- goto out;
- }
mutex_lock(&master->dev->mode_config.idr_mutex);
ret = _drm_lease_held_master(master, id);
mutex_unlock(&master->dev->mode_config.idr_mutex);
-out:
- drm_master_put(&master);
+ return ret;
+}
+
+bool drm_lease_held(struct drm_file *file_priv, int id)
+{
+ struct drm_master *master;
+ bool ret;
+
+ master = drm_file_get_master(file_priv);
+ ret = drm_lease_held_master(master, id);
+ if (master)
+ drm_master_put(&master);
+
return ret;
}
@@ -150,9 +153,6 @@ uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs_in)
int count_in, count_out;
uint32_t crtcs_out = 0;
- if (!file_priv)
- return crtcs_in;
-
master = drm_file_get_master(file_priv);
if (!master)
return crtcs_in;
diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index b5566167a798..af9f65bf74d4 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -23,6 +23,7 @@
#include <linux/slab.h>
#include <linux/uaccess.h>
+#include <drm/drm_auth.h>
#include <drm/drm_plane.h>
#include <drm/drm_drv.h>
#include <drm/drm_print.h>
@@ -687,6 +688,7 @@ int drm_mode_getplane(struct drm_device *dev, void *data,
struct drm_mode_get_plane *plane_resp = data;
struct drm_plane *plane;
uint32_t __user *format_ptr;
+ struct drm_master *master;
if (!drm_core_check_feature(dev, DRIVER_MODESET))
return -EOPNOTSUPP;
@@ -695,10 +697,13 @@ int drm_mode_getplane(struct drm_device *dev, void *data,
if (!plane)
return -ENOENT;
+ master = drm_file_get_master(file_priv);
drm_modeset_lock(&plane->mutex, NULL);
- if (plane->state && plane->state->crtc && drm_lease_held(file_priv, plane->state->crtc->base.id))
+ if (plane->state && plane->state->crtc &&
+ drm_lease_held_master(master, plane->state->crtc->base.id))
plane_resp->crtc_id = plane->state->crtc->base.id;
- else if (!plane->state && plane->crtc && drm_lease_held(file_priv, plane->crtc->base.id))
+ else if (!plane->state && plane->crtc &&
+ drm_lease_held_master(master, plane->crtc->base.id))
plane_resp->crtc_id = plane->crtc->base.id;
else
plane_resp->crtc_id = 0;
@@ -710,6 +715,8 @@ int drm_mode_getplane(struct drm_device *dev, void *data,
else
plane_resp->fb_id = 0;
drm_modeset_unlock(&plane->mutex);
+ if (master)
+ drm_master_put(&master);
plane_resp->plane_id = plane->base.id;
plane_resp->possible_crtcs = drm_lease_filter_crtcs(file_priv,
@@ -1114,6 +1121,7 @@ static int drm_mode_cursor_common(struct drm_device *dev,
return -ENOENT;
}
+ lockdep_assert_held_once(&dev->master_rwsem);
drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
retry:
ret = drm_modeset_lock(&crtc->mutex, &ctx);
@@ -1128,7 +1136,7 @@ static int drm_mode_cursor_common(struct drm_device *dev,
if (ret)
goto out;
- if (!drm_lease_held(file_priv, crtc->cursor->base.id)) {
+ if (file_priv && !drm_lease_held_master(file_priv->master, crtc->cursor->base.id)) {
ret = -EACCES;
goto out;
}
diff --git a/include/drm/drm_lease.h b/include/drm/drm_lease.h
index 5c9ef6a2aeae..426ea86d3c6a 100644
--- a/include/drm/drm_lease.h
+++ b/include/drm/drm_lease.h
@@ -18,6 +18,8 @@ bool drm_lease_held(struct drm_file *file_priv, int id);
bool _drm_lease_held(struct drm_file *file_priv, int id);
+bool drm_lease_held_master(struct drm_master *master, int id);
+
void drm_lease_revoke(struct drm_master *master);
uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs);
--
2.25.1
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