[PATCH] Revert "drm: add a locked version of drm_is_current_master"

* [PATCH] Revert "drm: add a locked version of drm_is_current_master"
@ 2021-06-22  7:54 ` Daniel Vetter
  0 siblings, 0 replies; 22+ messages in thread
From: Daniel Vetter @ 2021-06-22  7:54 UTC (permalink / raw)
  To: Intel Graphics Development
  Cc: DRI Development, Daniel Vetter, Desmond Cheong Zhi Xi,
	Emil Velikov, stable, Daniel Vetter, Maarten Lankhorst,
	Maxime Ripard, Thomas Zimmermann, David Airlie, Daniel Vetter

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);
*** DEADLOCK ***
1 lock held by kms_frontbuffer/1087:
 #0: ffff88810dcd0488 (&dev->mode_config.mutex){+.+.}-{3:3}, at: drm_mode_getconnector+0x1c6/0x4a0
stack backtrace:
CPU: 7 PID: 1087 Comm: kms_frontbuffer Not tainted 5.13.0-rc7-CI-CI_DRM_10254+ #1
Hardware name: Intel Corporation Ice Lake Client Platform/IceLake U DDR4 SODIMM PD RVP TLC, BIOS ICLSFWR1.R00.3234.A01.1906141750 06/14/2019
Call Trace:
 dump_stack+0x7f/0xad
 check_noncircular+0x12e/0x150
 __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

daniel@phenom:~/linux/drm-misc-fixes$ dim fixes 1815d9c86e3090477fbde066ff314a7e9721ee0f
Fixes: 1815d9c86e30 ("drm: add a locked version of drm_is_current_master")
Cc: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
---
 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 @@ void drm_master_release(struct drm_file *file_priv)
 	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
-- 
2.32.0.rc2


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