On 22/6/21 3:54 pm, Daniel Vetter wrote:
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 ***
Hi Daniel,
Just a thought.
Since &dev->mode_config.mutex is the modeset BKL and its scope isn't
clear, keeping the dependency as is would mean that any lock that
depends on &dev->mode_config.mutex would also depend on
&client->modeset_mutex. Seems like this might be vulnerable to more
circular dependencies.
Would it make sense to invert the locking dependency for
&client->modeset_mutex and &dev->mode_config.mutex to become
&dev->mode_config.mutex --> &client->modeset_mutex? Something like this:
diff --git a/drivers/gpu/drm/drm_client_modeset.c
b/drivers/gpu/drm/drm_client_modeset.c
index ced09c7c06f9..859f99d97cde 100644
--- a/drivers/gpu/drm/drm_client_modeset.c
+++ b/drivers/gpu/drm/drm_client_modeset.c
@@ -811,9 +811,9 @@ int drm_client_modeset_probe(struct drm_client_dev
*client, unsigned int width,
goto out;
}
+ mutex_lock(&dev->mode_config.mutex);
mutex_lock(&client->modeset_mutex);
- mutex_lock(&dev->mode_config.mutex);
for (i = 0; i < connector_count; i++)
total_modes_count += connectors[i]->funcs->fill_modes(connectors[i],
width, height);
if (!total_modes_count)
@@ -838,7 +838,6 @@ int drm_client_modeset_probe(struct drm_client_dev
*client, unsigned int width,
drm_client_pick_crtcs(client, connectors, connector_count,
crtcs, modes, 0, width, height);
}
- mutex_unlock(&dev->mode_config.mutex);
drm_client_modeset_release(client);
@@ -869,6 +868,7 @@ int drm_client_modeset_probe(struct drm_client_dev
*client, unsigned int width,
}
mutex_unlock(&client->modeset_mutex);
+ mutex_unlock(&dev->mode_config.mutex);
out:
kfree(crtcs);
kfree(modes);
diff --git a/drivers/gpu/drm/drm_fb_helper.c
b/drivers/gpu/drm/drm_fb_helper.c
index f6baa2046124..74302d110609 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1443,8 +1443,8 @@ static int pan_display_legacy(struct
fb_var_screeninfo *var,
struct drm_mode_set *modeset;
int ret = 0;
- mutex_lock(&client->modeset_mutex);
drm_modeset_lock_all(fb_helper->dev);
+ mutex_lock(&client->modeset_mutex);
drm_client_for_each_modeset(modeset, client) {
modeset->x = var->xoffset;
modeset->y = var->yoffset;
@@ -1457,8 +1457,8 @@ static int pan_display_legacy(struct
fb_var_screeninfo *var,
}
}
}
- drm_modeset_unlock_all(fb_helper->dev);
mutex_unlock(&client->modeset_mutex);
+ drm_modeset_unlock_all(fb_helper->dev);
return ret;
}
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 <[email protected]>
Cc: Emil Velikov <[email protected]>
Cc: [email protected]
Signed-off-by: Daniel Vetter <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>
---
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
