Subject: RCU stall on panda

From: [email-masked] (Paul E. McKenney)
Date: Mon, 5 May 2014 11:06:17 -0700

On Mon, May 05, 2014 at 05:39:43PM +0800, Alex Shi wrote:
> I keep seeing the RCU stall problem on panda board from 3.10 kernel to latest upstream kernel
> and google find some one report it before: https://lkml.org/lkml/2012/9/20/519
> 
> Is it the hardware issue or a real software problem?

I cannot distinguish between hardware and software from the trace below,
but given that you are also seeing a soft lockup, either way you do
appear to have a real problem as opposed to an RCU CPU stall warning
false positive.

							Thanx, Paul

>   95.519653] INFO: rcu_sched self-detected stall on CPU^M
> [   95.519866]  1: (1 GPs behind) idle=2e7/1/0 softirq=4404/4405 ^M
> [   95.526489] INFO: rcu_sched detected stalls on CPUs/tasks:^M
> [   95.526489]  1: (1 GPs behind) idle=2e7/1/0 softirq=4404/4405 ^M
> [   95.526489]  (detected by 0, t=4229 jiffies, g=800, c=799, q=440)^M
> [   95.526519] Task dump for CPU 1:^M
> [   95.526519] swapper/1       R running      0     0      1 0x00000000^M
> [   95.559844]   (t=4229 jiffies g=800 c=799 q=440)^M
> [   95.564727] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.15.0-rc4 #93^M
> [   95.571502] [<c00133fd>] (unwind_backtrace) from [<c001076d>] (show_stack+0x11/0x14)^M
> [   95.579711] [<c001076d>] (show_stack) from [<c0570465>] (dump_stack+0x75/0x88)^M
> [   95.587371] [<c0570465>] (dump_stack) from [<c0084383>] (rcu_check_callbacks+0x353/0x79c)^M
> [   95.596038] [<c0084383>] (rcu_check_callbacks) from [<c003e99f>] (update_process_times+0x33/0x4c)^M
> [   95.605438] [<c003e99f>] (update_process_times) from [<c008e5a3>] (tick_sched_handle.isra.18+0x1f/0x48)^M
> [   95.615386] [<c008e5a3>] (tick_sched_handle.isra.18) from [<c008e609>] (tick_sched_timer+0x3d/0x5c)^M
> [   95.624969] [<c008e609>] (tick_sched_timer) from [<c0051a23>] (__run_hrtimer+0x67/0x310)^M
> [   95.633544] [<c0051a23>] (__run_hrtimer) from [<c00525fd>] (hrtimer_interrupt+0xe1/0x214)^M
> [   95.642211] [<c00525fd>] (hrtimer_interrupt) from [<c008cecb>] (tick_receive_broadcast+0x1f/0x30)^M
> [   95.651611] [<c008cecb>] (tick_receive_broadcast) from [<c0011e4f>] (handle_IPI+0xb3/0x120)^M
> [   95.660461] [<c0011e4f>] (handle_IPI) from [<c00085e5>] (gic_handle_irq+0x51/0x54)^M
> [   95.668487] [<c00085e5>] (gic_handle_irq) from [<c057603f>] (__irq_svc+0x3f/0x64)^M
> [   95.676391] Exception stack(0xee0dbf10 to 0xee0dbf58)^M
> [   95.681762] bf00:                                     00000001 00000001 00000000 ee0d8c40^M
> [   95.690429] bf20: 3c6bd296 00000016 3c6f8c43 00000016 eefab540 c08e0c84 00000000 c0fc7114^M
> [   95.699066] bf40: 00000010 ee0dbf58 c006ef4d c0443890 40000033 ffffffff^M
> [   95.706085] [<c057603f>] (__irq_svc) from [<c0443890>] (cpuidle_enter_state+0xc0/0xc4)^M
> [   95.714477] [<c0443890>] (cpuidle_enter_state) from [<c0444d11>] (cpuidle_enter_state_coupled+0xe1/0x290)^M
> [   95.724639] [<c0444d11>] (cpuidle_enter_state_coupled) from [<c0067cd1>] (cpu_startup_entry+0x1a5/0x494)^M
> [   95.734680] [<c0067cd1>] (cpu_startup_entry) from [<80008685>] (0x80008685)^M
> [   95.742095] BUG: soft lockup - CPU#1 stuck for 40s! [swapper/1:0]^M
> [   95.748535] Modules linked in:^M
> [   95.751770] irq event stamp: 128730^M
> [   95.755462] hardirqs last  enabled at (128727): [<c044388f>] cpuidle_enter_state+0xbf/0xc4^M
> [   95.764221] hardirqs last disabled at (128728): [<c0576033>] __irq_svc+0x33/0x64^M
> [   95.772064] softirqs last  enabled at (128730): [<c00386cd>] irq_enter+0x59/0x60^M
> [   95.779907] softirqs last disabled at (128729): [<c00386ba>] irq_enter+0x46/0x60^M
> [   95.787750] ^M
> 
> 
> my RCU and IDLE related kernel config as blow:
> 
> CONFIG_TREE_RCU=y
> CONFIG_RCU_STALL_COMMON=y
> CONFIG_RCU_FANOUT=32
> CONFIG_RCU_FANOUT_LEAF=16
> CONFIG_TREE_RCU_TRACE=y
> CONFIG_PROVE_RCU=y
> CONFIG_PROVE_RCU_REPEATEDLY=y
> CONFIG_SPARSE_RCU_POINTER=y
> CONFIG_RCU_CPU_STALL_TIMEOUT=21
> CONFIG_RCU_CPU_STALL_INFO=y
> CONFIG_RCU_TRACE=y
> alexs at alex-panda:~$ cat /proc/config.gz | gunzip | grep IDLE
> CONFIG_NO_HZ_IDLE=y
> CONFIG_GENERIC_SMP_IDLE_THREAD=y
> CONFIG_GENERIC_IDLE_POLL_SETUP=y
> CONFIG_CPU_IDLE=y
> CONFIG_CPU_IDLE_GOV_LADDER=y
> CONFIG_CPU_IDLE_GOV_MENU=y
> CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED=y
> 
> -- 
> Thanks
>     Alex
>