Hi! There is a bug somewhere and I have already spent too much time whacking the mole. Need some hints, ideas on how to debug, etc. So, my setup is that: platform: Intel Merrifield USB host and device controller: DWC3 USB host connected device: Diolan DLN-2 IO expander In device mode: USB EEM The workflow ~~~~~~~~~~ The following steps to reproduce the issue (with some patches applied / reverted it may give different results from less than 10% up to almost 100% of reproducibility): (Note the board has a manual switch of an ID pin and two connectors depending on the role) 1. Connect the DLN-2 to USB A 2. Connect the PC machine to USB micro-B 3. Boot the board in device mode 4. Setup USB EEM gadget via ConfigFS 5. Turn the switch (see above note) to the host and back to the device mode as many times (usually a very few are needed) and with (semi-)arbitrary time in between (usually 2-5 seconds) till the issue occurs. The issue ~~~~~~~~ When switching from the host to the gadget mode - the status LED on the DLN-2 board continues blinking (Vbus is on) - the driver may be still xhci (rarely), but often already switched to dwc3 - due to above `lsusb` (rarely) still shows hub devices - the EEM does not appear (PC doesn't see network iface) - in ~50% cases RCU stall (there are only two CPUs) RCU stall ~~~~~~~~ cat /proc/interrupts 16: 176129 0 IO-APIC 34-fasteoi xhci-hcd:usb1 [434689.740982] rcu: INFO: rcu_sched self-detected stall on CPU [434689.746856] rcu: 0-....: (24661 ticks this GP) idle=ee2/1/0x4000000000000000 softirq=4162/4163 fqs=5238 [434689.756867] (t=21000 jiffies g=8489 q=52) [434689.761204] NMI backtrace for cpu 0 [434689.764919] CPU: 0 PID: 222 Comm: kworker/0:0 Not tainted 5.13.0-rc5+ #4 [434689.771948] Hardware name: Intel Corporation Merrifield/BODEGA BAY, BIOS 542 2015.01.21:18.19.48 [434689.781126] Workqueue: usb_hub_wq hub_event [434689.785590] Call Trace: [434689.788232] <IRQ> [434689.790431] dump_stack+0x69/0x8e [434689.793996] nmi_cpu_backtrace.cold+0x32/0x69 [434689.798612] ? lapic_can_unplug_cpu+0x80/0x80 [434689.803249] nmi_trigger_cpumask_backtrace+0x8a/0xa0 [434689.808508] rcu_dump_cpu_stacks+0xbf/0xed [434689.812873] rcu_sched_clock_irq.cold+0xc7/0x1e9 [434689.817805] update_process_times+0x8c/0xc0 [434689.822255] tick_sched_handle+0x34/0x50 [434689.826432] tick_sched_timer+0x7a/0xd0 [434689.830513] ? get_cpu_iowait_time_us+0x110/0x110 [434689.835499] __hrtimer_run_queues+0x157/0x350 [434689.840171] hrtimer_interrupt+0x110/0x2c0 [434689.844569] __sysvec_apic_timer_interrupt+0x76/0x150 [434689.849911] sysvec_apic_timer_interrupt+0x2f/0x90 [434689.854990] asm_sysvec_apic_timer_interrupt+0x12/0x20 [434689.860415] RIP: 0010:_raw_spin_unlock_irqrestore+0x37/0x50 [434689.866294] Code: 53 48 89 f3 48 8b 74 24 10 e8 45 fa 3a ff 48 89 ef e8 6d 23 3b ff 9c 58 f6 c4 02 75 10 80 e7 02 74 01 fb 65 ff 0d e9 d3 4f 78 <5b> 5d c3 e8 b1 3b ff ff eb e9 66 66 2e 0f 1f 84 00 00 00 00 00 0f [434689.885773] RSP: 0000:ffff9ac140003da8 EFLAGS: 00000206 [434689.891294] RAX: 0000000000000046 RBX: 0000000000000202 RCX: ffff8b7e4ad208d0 [434689.898775] RDX: 0000000062c241c0 RSI: 0000000042fee84d RDI: ffffffff89460720 [434689.906255] RBP: ffffffff89460720 R08: 00000000897fe2f0 R09: 0000000000000001 [434689.913733] R10: 0000000000000000 R11: ffff8b7e46226db0 R12: ffff8b7e4b29c000 [434689.921214] R13: 0000000000000000 R14: ffff8b7e4b29c2f8 R15: ffff8b7e42e65780 [434689.928798] debug_dma_unmap_page+0x7e/0x90 [434689.933324] ? __lock_acquire.constprop.0+0x27d/0x550 [434689.938681] ? find_held_lock+0x2b/0x80 [434689.942787] usb_hcd_unmap_urb_for_dma+0x65/0x100 [434689.947785] __usb_hcd_giveback_urb+0x4b/0x100 [434689.952513] usb_giveback_urb_bh+0xa7/0x100 [434689.956994] tasklet_action_common.constprop.0+0xd0/0x140 [434689.962712] __do_softirq+0xeb/0x2dd [434689.966565] irq_exit_rcu+0x95/0xc0 [434689.970288] common_interrupt+0x7b/0xa0 [434689.974375] </IRQ> [434689.976670] asm_common_interrupt+0x1e/0x40 [434689.981109] RIP: 0010:_raw_spin_unlock_irq+0x27/0x30 [434689.986359] Code: 35 ff 90 0f 1f 44 00 00 55 48 8b 74 24 08 48 89 fd 48 8d 7f 18 e8 79 fa 3a ff 48 89 ef e8 a1 23 3b ff fb 65 ff 0d 29 d4 4f 78 <5d> c3 0f 1f 80 00 00 00 00 0f 1f 44 00 00 55 48 89 fd 48 83 c7 18 [434690.005836] RSP: 0000:ffff9ac140293b98 EFLAGS: 00000246 [434690.011352] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff8b7e4ad208d0 [434690.018832] RDX: 0000000062c241c0 RSI: 0000000042fee84d RDI: ffffffff8881ab00 [434690.026309] RBP: ffffffff8881ab00 R08: 00000000897fe2f0 R09: 0000000000000001 [434690.033790] R10: ffff8b7e7e23ac30 R11: 0000000000000000 R12: 0000000000000000 [434690.041268] R13: ffff8b7e4b29c000 R14: ffff8b7e4b40c018 R15: ffff8b7e4af62950 [434690.048840] ? _raw_spin_unlock_irq+0x1f/0x30 [434690.053465] usb_hcd_submit_urb+0x294/0xbf0 [434690.057948] ? lockdep_init_map_type+0x47/0x220 [434690.062805] usb_start_wait_urb+0x65/0x160 [434690.067230] usb_control_msg+0xdf/0x140 [434690.071355] hub_event+0x8f4/0x1890 [434690.075184] ? lock_acquire+0x93/0x150 [434690.079175] ? process_one_work+0x1bc/0x4b0 [434690.083652] process_one_work+0x24d/0x4b0 [434690.087970] worker_thread+0x55/0x3c0 [434690.091875] ? rescuer_thread+0x390/0x390 [434690.096154] kthread+0x137/0x150 [434690.099612] ? __kthread_bind_mask+0x60/0x60 [434690.104166] ret_from_fork+0x22/0x30 followed by Watchdog one [434725.296748] Kernel panic - not syncing: Kernel Watchdog [434725.302247] CPU: 0 PID: 222 Comm: kworker/0:0 Not tainted 5.13.0-rc5+ #4 [434725.309242] Hardware name: Intel Corporation Merrifield/BODEGA BAY, BIOS 542 2015.01.21:18.19.48 [434725.318367] Workqueue: usb_hub_wq hub_event [434725.322801] Call Trace: [434725.325424] <IRQ> [434725.327607] dump_stack+0x69/0x8e [434725.331145] panic+0x102/0x2d1 [434725.334460] mid_wdt_irq+0x11/0x11 [434725.338072] __handle_irq_event_percpu+0x65/0x1c0 [434725.343048] handle_irq_event+0x55/0xb0 [434725.347124] handle_fasteoi_irq+0x78/0x1d0 [434725.351461] __common_interrupt+0x3e/0xa0 [434725.355713] common_interrupt+0x3b/0xa0 [434725.359784] asm_common_interrupt+0x1e/0x40 [434725.364192] RIP: 0010:_raw_spin_lock_irqsave+0x0/0x50 [434725.369501] Code: 8d 7f 18 45 31 c9 31 c9 41 b8 01 00 00 00 31 d2 31 f6 e8 03 ff 3a ff 48 89 ef 58 5d e9 99 24 3b ff 66 0f 1f 84 00 00 00 00 00 <0f> 1f 44 00 00 41 54 55 48 89 fd 9c 41 5c fa 65 ff 05 ea d5 4f 78 [434725.388866] RSP: 0000:ffff9ac140003d00 EFLAGS: 00000202 [434725.394347] RAX: 0000000000000028 RBX: 00000000002b5ea8 RCX: ffff8b7e4ad208d0 [434725.401779] RDX: 0000000062c241c0 RSI: 0000000042fee84d RDI: ffffffff887579e0 [434725.409211] RBP: 0000000000000282 R08: 00000000897fe2f0 R09: 0000000000000001 [434725.416641] R10: 0000000000000000 R11: ffff8b7e46226db0 R12: ffff8b7e41282500 [434725.424073] R13: ffff8b7e41281f00 R14: 0000000000000200 R15: 000000000ad7aa00 [434725.431582] add_dma_entry+0xa9/0x1d0 [434725.435487] dma_map_page_attrs+0xd8/0x220 [434725.439847] usb_hcd_map_urb_for_dma+0x3b6/0x4f0 [434725.444734] usb_hcd_submit_urb+0x98/0xbf0 [434725.449059] ? __lock_acquire.constprop.0+0x27d/0x550 [434725.454378] ? find_held_lock+0x2b/0x80 [434725.458493] dln2_rx+0x1d6/0x2b0 [dln2] [434725.462595] __usb_hcd_giveback_urb+0x91/0x100 [434725.467291] usb_giveback_urb_bh+0xa7/0x100 [434725.471740] tasklet_action_common.constprop.0+0xd0/0x140 [434725.477420] __do_softirq+0xeb/0x2dd [434725.481240] irq_exit_rcu+0x95/0xc0 [434725.484939] common_interrupt+0x7b/0xa0 [434725.489000] </IRQ> [434725.491275] asm_common_interrupt+0x1e/0x40 [434725.495682] RIP: 0010:_raw_spin_unlock_irq+0x27/0x30 [434725.500898] Code: 35 ff 90 0f 1f 44 00 00 55 48 8b 74 24 08 48 89 fd 48 8d 7f 18 e8 79 fa 3a ff 48 89 ef e8 a 1 23 3b ff fb 65 ff 0d 29 d4 4f 78 <5d> c3 0f 1f 80 00 00 00 00 0f 1f 44 00 00 55 48 89 fd 48 83 c7 18 [434725.520261] RSP: 0000:ffff9ac140293b98 EFLAGS: 00000246 [434725.525742] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff8b7e4ad208d0 [434725.533174] RDX: 0000000062c241c0 RSI: 0000000042fee84d RDI: ffffffff8881ab00 [434725.540606] RBP: ffffffff8881ab00 R08: 00000000897fe2f0 R09: 0000000000000001 [434725.548037] R10: ffff8b7e7e23ac30 R11: 0000000000000000 R12: 0000000000000000 [434725.555469] R13: ffff8b7e4b29c000 R14: ffff8b7e4b40c018 R15: ffff8b7e4af62950 [434725.562975] ? _raw_spin_unlock_irq+0x1f/0x30 [434725.567571] usb_hcd_submit_urb+0x294/0xbf0 [434725.572017] ? lockdep_init_map_type+0x47/0x220 [434725.576831] usb_start_wait_urb+0x65/0x160 [434725.581213] usb_control_msg+0xdf/0x140 [434725.585302] hub_event+0x8f4/0x1890 [434725.589087] ? lock_acquire+0x93/0x150 [434725.593053] ? process_one_work+0x1bc/0x4b0 [434725.597494] process_one_work+0x24d/0x4b0 [434725.601776] worker_thread+0x55/0x3c0 [434725.605657] ? rescuer_thread+0x390/0x390 [434725.609904] kthread+0x137/0x150 [434725.613342] ? __kthread_bind_mask+0x60/0x60 [434725.617862] ret_from_fork+0x22/0x30 [434725.622038] Kernel Offset: 0x5e00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) [434725.633177] ---[ end Kernel panic - not syncing: Kernel Watchdog ]--- Any ideas, hints, etc are welcome! -- With Best Regards, Andy Shevchenko
