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Message-Id: <20210628141828.31757-106-sashal@kernel.org>
Date: Mon, 28 Jun 2021 10:18:23 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Daniel Vetter <daniel.vetter@...ll.ch>
Subject: [PATCH 5.12 105/110] Revert "drm: add a locked version of drm_is_current_master"
From: Daniel Vetter <daniel.vetter@...ll.ch>
commit f54b3ca7ea1e5e02f481cf4ca54568e57bd66086 upstream.
This reverts commit 1815d9c86e3090477fbde066ff314a7e9721ee0f.
Unfortunately this inverts the locking hierarchy, so back to the
drawing board. Full lockdep splat below:
======================================================
WARNING: possible circular locking dependency detected
5.13.0-rc7-CI-CI_DRM_10254+ #1 Not tainted
------------------------------------------------------
kms_frontbuffer/1087 is trying to acquire lock:
ffff88810dcd01a8 (&dev->master_mutex){+.+.}-{3:3}, at: drm_is_current_master+0x1b/0x40
but task is already holding lock:
ffff88810dcd0488 (&dev->mode_config.mutex){+.+.}-{3:3}, at: drm_mode_getconnector+0x1c6/0x4a0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&dev->mode_config.mutex){+.+.}-{3:3}:
__mutex_lock+0xab/0x970
drm_client_modeset_probe+0x22e/0xca0
__drm_fb_helper_initial_config_and_unlock+0x42/0x540
intel_fbdev_initial_config+0xf/0x20 [i915]
async_run_entry_fn+0x28/0x130
process_one_work+0x26d/0x5c0
worker_thread+0x37/0x380
kthread+0x144/0x170
ret_from_fork+0x1f/0x30
-> #1 (&client->modeset_mutex){+.+.}-{3:3}:
__mutex_lock+0xab/0x970
drm_client_modeset_commit_locked+0x1c/0x180
drm_client_modeset_commit+0x1c/0x40
__drm_fb_helper_restore_fbdev_mode_unlocked+0x88/0xb0
drm_fb_helper_set_par+0x34/0x40
intel_fbdev_set_par+0x11/0x40 [i915]
fbcon_init+0x270/0x4f0
visual_init+0xc6/0x130
do_bind_con_driver+0x1e5/0x2d0
do_take_over_console+0x10e/0x180
do_fbcon_takeover+0x53/0xb0
register_framebuffer+0x22d/0x310
__drm_fb_helper_initial_config_and_unlock+0x36c/0x540
intel_fbdev_initial_config+0xf/0x20 [i915]
async_run_entry_fn+0x28/0x130
process_one_work+0x26d/0x5c0
worker_thread+0x37/0x380
kthread+0x144/0x170
ret_from_fork+0x1f/0x30
-> #0 (&dev->master_mutex){+.+.}-{3:3}:
__lock_acquire+0x151e/0x2590
lock_acquire+0xd1/0x3d0
__mutex_lock+0xab/0x970
drm_is_current_master+0x1b/0x40
drm_mode_getconnector+0x37e/0x4a0
drm_ioctl_kernel+0xa8/0xf0
drm_ioctl+0x1e8/0x390
__x64_sys_ioctl+0x6a/0xa0
do_syscall_64+0x39/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xae
other info that might help us debug this:
Chain exists of: &dev->master_mutex --> &client->modeset_mutex --> &dev->mode_config.mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&dev->mode_config.mutex);
lock(&client->modeset_mutex);
lock(&dev->mode_config.mutex);
lock(&dev->master_mutex);
---
drivers/gpu/drm/drm_auth.c | 51 ++++++++++++++------------------------
1 file changed, 19 insertions(+), 32 deletions(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index 86d4b72e95cb..232abbba3686 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -61,35 +61,6 @@
* trusted clients.
*/
-static bool drm_is_current_master_locked(struct drm_file *fpriv)
-{
- lockdep_assert_held_once(&fpriv->master->dev->master_mutex);
-
- return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
-}
-
-/**
- * drm_is_current_master - checks whether @priv is the current master
- * @fpriv: DRM file private
- *
- * Checks whether @fpriv is current master on its device. This decides whether a
- * client is allowed to run DRM_MASTER IOCTLs.
- *
- * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting
- * - the current master is assumed to own the non-shareable display hardware.
- */
-bool drm_is_current_master(struct drm_file *fpriv)
-{
- bool ret;
-
- mutex_lock(&fpriv->master->dev->master_mutex);
- ret = drm_is_current_master_locked(fpriv);
- mutex_unlock(&fpriv->master->dev->master_mutex);
-
- return ret;
-}
-EXPORT_SYMBOL(drm_is_current_master);
-
int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
{
struct drm_auth *auth = data;
@@ -252,7 +223,7 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
if (ret)
goto out_unlock;
- if (drm_is_current_master_locked(file_priv))
+ if (drm_is_current_master(file_priv))
goto out_unlock;
if (dev->master) {
@@ -301,7 +272,7 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
if (ret)
goto out_unlock;
- if (!drm_is_current_master_locked(file_priv)) {
+ if (!drm_is_current_master(file_priv)) {
ret = -EINVAL;
goto out_unlock;
}
@@ -350,7 +321,7 @@ void drm_master_release(struct drm_file *file_priv)
if (file_priv->magic)
idr_remove(&file_priv->master->magic_map, file_priv->magic);
- if (!drm_is_current_master_locked(file_priv))
+ if (!drm_is_current_master(file_priv))
goto out;
drm_legacy_lock_master_cleanup(dev, master);
@@ -371,6 +342,22 @@ out:
mutex_unlock(&dev->master_mutex);
}
+/**
+ * drm_is_current_master - checks whether @priv is the current master
+ * @fpriv: DRM file private
+ *
+ * Checks whether @fpriv is current master on its device. This decides whether a
+ * client is allowed to run DRM_MASTER IOCTLs.
+ *
+ * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting
+ * - the current master is assumed to own the non-shareable display hardware.
+ */
+bool drm_is_current_master(struct drm_file *fpriv)
+{
+ return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
+}
+EXPORT_SYMBOL(drm_is_current_master);
+
/**
* drm_master_get - reference a master pointer
* @master: &struct drm_master
--
2.30.2
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