Hi,

the drm_fb_helper_hotplug_event() locks all crtc->mutex locks by calling drm_modeset_lock_all() and later calls drm_fb_helper_probe_connector_modes(), which in case of i915 DRM driver effectively calls intel_get_load_detect_pipe() that tries to lock crtc->mutex again. This causes a deadlock, and can be in some cases triggered by VT switch to framebuffer console on i915.

This bug is introduced in Linux 3.9-rc1 and still exists in v3.9-rc6-183-gbf81710. Linux 3.8 is ok.

This deadlock is probably introduced by commit 7b24056be6db7ce907baffdd4cf142ab774ea60c (drm: don't hold crtc mutexes for connector ->detect callbacks).

Steps to reproduce (the deadlock occurs in almost all cases): LCD panel connected to LVDS1, 915GM, HP nc6120 1. power on 2. $ startx 3. connect monitor to VGA1 4. $ xrandr --output VGA1 --mode 1600x1200 --right-of LVDS1 5. change VT, ALT + CTRL + F2

Krzysiek

... [ 62.995861] [drm:drm_helper_probe_single_connector_modes], [CONNECTOR:13:SVIDEO-1] [ 62.995870] [drm:intel_get_load_detect_pipe], [CONNECTOR:13:SVIDEO-1], [ENCODER:14:TV-14] [ 62.995873] [ 62.995875] ============================================= [ 62.995877] [ INFO: possible recursive locking detected ] [ 62.995881] 3.9.0-rc6-00184-gc875d9b #14 Not tainted # v3.9-rc6-183-gbf81710 + one unrelated local patch. [ 62.995883] --------------------------------------------- [ 62.995885] X/1759 is trying to acquire lock: [ 62.995903] (&crtc->mutex){+.+.+.}, at: [<803649e4>] intel_get_load_detect_pipe+0x164/0x3f0 [ 62.995905] [ 62.995905] but task is already holding lock: [ 62.995916] (&crtc->mutex){+.+.+.}, at: [<8032d1da>] drm_modeset_lock_all+0x3a/0x50 [ 62.995918] [ 62.995918] other info that might help us debug this: [ 62.995920] Possible unsafe locking scenario: [ 62.995920] [ 62.995921] CPU0 [ 62.995923] ---- [ 62.995926] lock(&crtc->mutex); [ 62.995930] lock(&crtc->mutex); [ 62.995931] [ 62.995931] *** DEADLOCK *** [ 62.995931] [ 62.995933] May be due to missing lock nesting notation [ 62.995933] [ 62.995936] 3 locks held by X/1759: [ 62.995948] #0: (console_lock){+.+.+.}, at: [<802fe726>] vt_ioctl+0xe26/0x1220 [ 62.995958] #1: (&dev->mode_config.mutex){+.+.+.}, at: [<8032d1b5>] drm_modeset_lock_all+0x15/0x50 [ 62.995968] #2: (&crtc->mutex){+.+.+.}, at: [<8032d1da>] drm_modeset_lock_all+0x3a/0x50 [ 62.995970] [ 62.995970] stack backtrace: [ 62.995974] Pid: 1759, comm: X Not tainted 3.9.0-rc6-00184-gc875d9b #14 [ 62.995976] Call Trace: [ 62.995985] [<8016d9f8>] __lock_acquire+0x748/0x19e0 [ 62.995991] [<80160008>] ? ktime_get+0xb8/0xf0 [ 62.995998] [<80155f6e>] ? local_clock+0x4e/0x60 [ 62.996005] [<8012c2c5>] ? log_store+0x2d5/0x3b0 [ 62.996011] [<8014fc83>] ? down_trylock+0x13/0x40 [ 62.996017] [<8016b655>] ? mark_held_locks+0x75/0xe0 [ 62.996020] [<8012d9b9>] ? vprintk_emit+0x159/0x4e0 [ 62.996020] [<8016f189>] lock_acquire+0x79/0x90 [ 62.996020] [<803649e4>] ? intel_get_load_detect_pipe+0x164/0x3f0 [ 62.996020] [<8050acf4>] mutex_lock_nested+0x54/0x310 [ 62.996020] [<803649e4>] ? intel_get_load_detect_pipe+0x164/0x3f0 [ 62.996020] [<803649e4>] ? intel_get_load_detect_pipe+0x164/0x3f0 [ 62.996020] [<80327c7a>] ? drm_ut_debug_printk+0x2a/0x50 [ 62.996020] [<803649e4>] intel_get_load_detect_pipe+0x164/0x3f0 [ 62.996020] [<80108707>] ? native_sched_clock+0x27/0xb0 [ 62.996020] [<80155bcc>] ? sched_clock_local.constprop.2+0x3c/0x170 [ 62.996020] [<8038061d>] intel_tv_detect+0x15d/0x570 [ 62.996020] [<8016b98b>] ? trace_hardirqs_off+0xb/0x10 [ 62.996020] [<80155f6e>] ? local_clock+0x4e/0x60 [ 62.996020] [<8012c2c5>] ? log_store+0x2d5/0x3b0 [ 62.996020] [<8014fc83>] ? down_trylock+0x13/0x40 [ 62.996020] [<8031dbd8>] drm_helper_probe_single_connector_modes+0x278/0x330 [ 62.996020] [<80319fc7>] drm_fb_helper_probe_connector_modes.isra.3+0x37/0x60 [ 62.996020] [<8031bfec>] drm_fb_helper_hotplug_event+0x6c/0xc0 [ 62.996020] [<8031c0d3>] drm_fb_helper_set_par+0x93/0xc0 [ 62.996020] [<802afdaa>] fb_set_var+0x1ea/0x4b0 [ 62.996020] [<8016d6bb>] ? __lock_acquire+0x40b/0x19e0 [ 62.996020] [<80108707>] ? native_sched_clock+0x27/0xb0 [ 62.996020] [<80155bcc>] ? sched_clock_local.constprop.2+0x3c/0x170 [ 62.996020] [<802b964a>] fbcon_blank+0x2aa/0x300 [ 62.996020] [<80307371>] do_unblank_screen+0x91/0x1a0 [ 62.996020] [<802fd876>] complete_change_console+0x56/0xe0 [ 62.996020] [<802fea3f>] vt_ioctl+0x113f/0x1220 [ 62.996020] [<8050d8c7>] ? _raw_spin_unlock+0x27/0x50 [ 62.996020] [<802fd900>] ? complete_change_console+0xe0/0xe0 [ 62.996020] [<802f438a>] tty_ioctl+0x26a/0xb70 [ 62.996020] [<80155bcc>] ? sched_clock_local.constprop.2+0x3c/0x170 [ 62.996020] [<802fd900>] ? complete_change_console+0xe0/0xe0 [ 62.996020] [<80155db5>] ? sched_clock_cpu+0x75/0xd0 [ 62.996020] [<8016b98b>] ? trace_hardirqs_off+0xb/0x10 [ 62.996020] [<80155f6e>] ? local_clock+0x4e/0x60 [ 62.996020] [<80169a2d>] ? put_lock_stats.isra.22+0xd/0x30 [ 62.996020] [<802f4120>] ? no_tty+0x20/0x20 [ 62.996020] [<801ca9c3>] do_vfs_ioctl+0x73/0x5d0 [ 62.996020] [<8014ede6>] ? up_read+0x16/0x30 [ 62.996020] [<8012548b>] ? __do_page_fault+0x1bb/0x470 [ 62.996020] [<801d6f18>] ? fget_light+0x2c8/0x410 [ 62.996020] [<8022fcc0>] ? reiserfs_sync_file+0x120/0x120 [ 62.996020] [<801caf57>] sys_ioctl+0x37/0x80 [ 62.996020] [<8050eb78>] sysenter_do_call+0x12/0x36