Den 11.06.2019 14.37, skrev Daniel Vetter:
> On Tue, Jun 11, 2019 at 01:57:16PM +0200, Thomas Zimmermann wrote:
>> Acquiring drm_client_dev.modeset_mutex after the locks in drm_fb_helper.dev
>> creates a deadlock with drm_setup_crtcs() as shown below:
>>
>> [ 4.959319] fbcon: radeondrmfb (fb0) is primary device
>> [ 4.993952] Console: switching to colour frame buffer device 240x67
>> [ 4.994040]
>> [ 4.994041] ======================================================
>> [ 4.994041] WARNING: possible circular locking dependency detected
>> [ 4.994042] 5.2.0-rc4-1-default+ #39 Tainted: G E
>> [ 4.994043] ------------------------------------------------------
>> [ 4.994043] systemd-udevd/369 is trying to acquire lock:
>> [ 4.994044] 00000000fb622acb (&client->modeset_mutex){+.+.}, at: drm_fb_helper_pan_display+0x103/0x1f0 [drm_kms_helper]
>> [ 4.994055]
>> [ 4.994055] but task is already holding lock:
>> [ 4.994055] 0000000028767ae4 (crtc_ww_class_mutex){+.+.}, at: drm_modeset_lock+0x42/0xf0 [drm]
>> [ 4.994072]
>> [ 4.994072] which lock already depends on the new lock.
>> [ 4.994072]
>> [ 4.994072]
>> [ 4.994072] the existing dependency chain (in reverse order) is:
>> [ 4.994073]
>> [ 4.994073] -> #3 (crtc_ww_class_mutex){+.+.}:
>> [ 4.994076] lock_acquire+0x9e/0x170
>> [ 4.994079] __ww_mutex_lock.constprop.18+0x97/0xf40
>> [ 4.994080] ww_mutex_lock+0x30/0x90
>> [ 4.994091] drm_modeset_lock+0x42/0xf0 [drm]
>> [ 4.994102] drm_modeset_lock_all_ctx+0x1f/0xe0 [drm]
>> [ 4.994113] drm_modeset_lock_all+0x5e/0x1a0 [drm]
>> [ 4.994163] intel_modeset_init+0x60b/0xda0 [i915]
>> ..
>> [ 4.994253]
>> [ 4.994253] -> #2 (crtc_ww_class_acquire){+.+.}:
>> [ 4.994255] lock_acquire+0x9e/0x170
>> [ 4.994270] drm_modeset_acquire_init+0xcc/0x100 [drm]
>> [ 4.994280] drm_modeset_lock_all+0x44/0x1a0 [drm]
>> [ 4.994320] intel_modeset_init+0x60b/0xda0 [i915]
>> ..
>> [ 4.994403]
>> [ 4.994403] -> #1 (&dev->mode_config.mutex){+.+.}:
>> [ 4.994405] lock_acquire+0x9e/0x170
>> [ 4.994408] __mutex_lock+0x62/0x8c0
>> [ 4.994413] drm_setup_crtcs+0x17c/0xc50 [drm_kms_helper]
>> [ 4.994418] __drm_fb_helper_initial_config_and_unlock+0x34/0x530 [drm_kms_helper]
>> [ 4.994450] radeon_fbdev_init+0x110/0x130 [radeon]
>> ..
>> [ 4.994535]
>> [ 4.994535] -> #0 (&client->modeset_mutex){+.+.}:
>> [ 4.994537] __lock_acquire+0xa85/0xe90
>> [ 4.994538] lock_acquire+0x9e/0x170
>> [ 4.994540] __mutex_lock+0x62/0x8c0
>> [ 4.994545] drm_fb_helper_pan_display+0x103/0x1f0 [drm_kms_helper]
>> [ 4.994547] fb_pan_display+0x92/0x120
>> [ 4.994549] bit_update_start+0x1a/0x40
>> [ 4.994550] fbcon_switch+0x392/0x580
>> [ 4.994552] redraw_screen+0x12c/0x220
>> [ 4.994553] do_bind_con_driver.cold.30+0xe1/0x10d
>> [ 4.994554] do_take_over_console+0x113/0x190
>> [ 4.994555] do_fbcon_takeover+0x58/0xb0
>> [ 4.994557] notifier_call_chain+0x47/0x70
>> [ 4.994558] blocking_notifier_call_chain+0x44/0x60
>> [ 4.994559] register_framebuffer+0x231/0x310
>> [ 4.994564] __drm_fb_helper_initial_config_and_unlock+0x2fd/0x530 [drm_kms_helper]
>> [ 4.994590] radeon_fbdev_init+0x110/0x130 [radeon]
>> ..
>>
>> This problem was introduced in
>>
>> d81294afe drm/fb-helper: Remove drm_fb_helper_crtc
>>
>> Reversing the lock ordering in pan_display_legacy() fixes the issue. The fix
>> was suggested by Daniel Vetter.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
>> Fixes: d81294afeecdacc8d84804ba0bcb3d39e64d0f27
>
> I think for ocd consistency it be nice to pull the lock out from both
> pan_display_atomic and pan_disaply_legacy and move it into
> drm_fb_helper_pan_display. Like we do drm_fb_helper_dpms or
> drm_fb_helper_setcmap or restore_fbdev_mode_force.
Is 'lock' referring to modeset_mutex? If so it can't be moved out
because pan_display_atomic() calls drm_client_modeset_commit_force()
which in turn takes the modeset_mutex lock.
The locking in _pan_display isn't so nice looking, but I figured that no
other client would need to do panning so I kept the ugliness in
drm_fb_helper instead of adding complexity to drm_client.
Thanks for fixing this Thomas.
Do you have commit rights or should I apply this?
Acked-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
Noralf.
>
> Either way Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>
>> ---
>> drivers/gpu/drm/drm_fb_helper.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>> index 7b388674a456..d6991f07cb17 100644
>> --- a/drivers/gpu/drm/drm_fb_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>> @@ -1586,8 +1586,8 @@ static int pan_display_legacy(struct fb_var_screeninfo *var,
>> struct drm_mode_set *modeset;
>> int ret = 0;
>>
>> - drm_modeset_lock_all(fb_helper->dev);
>> mutex_lock(&client->modeset_mutex);
>> + drm_modeset_lock_all(fb_helper->dev);
>> drm_client_for_each_modeset(modeset, client) {
>> modeset->x = var->xoffset;
>> modeset->y = var->yoffset;
>> @@ -1600,8 +1600,8 @@ static int pan_display_legacy(struct fb_var_screeninfo *var,
>> }
>> }
>> }
>> - mutex_unlock(&client->modeset_mutex);
>> drm_modeset_unlock_all(fb_helper->dev);
>> + mutex_unlock(&client->modeset_mutex);
>>
>> return ret;
>> }
>> --
>> 2.21.0
>>
>
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