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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 ind81294afedrm/fb-helper: Remove drm_fb_helper_crtc Reversing the lock ordering in pan_display_legacy() fixes the issue. Fixes:d81294afee("drm/fb-helper: Remove drm_fb_helper_crtc") Cc: Noralf Trønnes <noralf@tronnes.org> Cc: Sam Ravnborg <sam@ravnborg.org> Cc: David Airlie <airlied@linux.ie> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Cc: Maxime Ripard <maxime.ripard@bootlin.com> Cc: Sean Paul <sean@poorly.run> Cc: dri-devel@lists.freedesktop.org Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20190611115716.7052-1-tzimmermann@suse.de
Linux kernel
============
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