[PATCH] Revert "drm: add a locked version of drm_is_current_master"
Desmond Cheong Zhi Xi
desmondcheongzx at gmail.com
Wed Jun 23 08:09:11 UTC 2021
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 at 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 at gmail.com>
> Cc: Emil Velikov <emil.l.velikov at gmail.com>
> Cc: stable at vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel at 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
>
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