Commits
Thomas Zimmermann committed 1ff30dd85e6
drm: Reverse lock order in pan_display_legacy()
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.
Fixes: d81294afeecd ("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