Subject: arm64 function_graph tracer panic with CONFIG_DYNAMIC_FTRACE

From: [email-masked] (AKASHI Takahiro)
Date: Fri, 13 Nov 2015 14:51:07 +0900

Catalin,
(add lakml back to Cc)

On 11/13/2015 01:01 AM, Catalin Marinas wrote:
 > On Fri, Nov 13, 2015 at 12:00:42AM +0900, AKASHI Takahiro wrote:
 >> If possible, please try again with "select HAVE_FUNCTION_GRAPH_FP_TEST" added
 >> to CONFIG_ARM64.
 >> It will insert an additional check. I hope this will help.
 >
 > So it looks the the frame is off by some amount:

I was able to reproduce the problem on hikey, too.

 > # echo function_graph > /sys/kernel/debug/tracing/current_tracer
 > Bad frame pointer: expected ffffffc976b3bd50, received ffffffc976b3be60

The difference of fp's was 0x110(sizeof(pt_reg_t)=0x120).
It seems that an interrupt happened here (and we might have unwound one extra frame?).

 >    from func psci_cpu_suspend return to ffffffc00008d058

Always in the same place.

 > ------------[ cut here ]------------
 > WARNING: at /work/Linux/linux-2.6-aarch64/kernel/trace/trace_functions_graph.c:223
 > Modules linked in:
 >
 > CPU: 4 PID: 0 Comm: swapper/4 Not tainted 4.3.0+ #584
 > Hardware name: Juno (DT)
 > task: ffffffc976b22f00 ti: ffffffc976b38000 task.ti: ffffffc976b38000
 > PC is at ftrace_return_to_handler+0x11c/0x150
 > LR is at ftrace_return_to_handler+0x11c/0x150
 > pc : [<ffffffc000172034>] lr : [<ffffffc000172034>] pstate: 800001c5
 > sp : ffffffc976b3bdd0
 > x29: ffffffc976b3bdd0 x28: ffffffc0006c9000
 > x27: ffffffc000a29f20 x26: ffffffc976b3bf70
 > x25: 000000cc2c13e054 x24: 0000000000000004
 > x23: ffffffc000aeb790 x22: 0000000000000002
 > x21: ffffffc975503200 x20: ffffffc000aeb850
 > x19: 0000000000000002 x18: ffffffc000b3a920
 > x17: 0000000000000000 x16: 0000000000000000
 > x15: ffffffc000b3a5bf x14: 3739636666666666
 > x13: 6620646576696563 x12: 6572202c30356462
 > x11: 3362363739636666 x10: 00000000000000fc
 > x9 : ffffffc9768070c0 x8 : 0000000000001dd0
 > x7 : ffffffc9760f4c80 x6 : ffffffc9760f4c00
 > x5 : 00000000000084c0 x4 : 0000000000000001
 > x3 : ffffffc976b3bc50 x2 : 0000000000000001
 > x1 : 000000000000007f x0 : 000000000000007f
 >
 > ---[ end trace ac97c44ba7dabcce ]---
 > Call trace:
 > [<ffffffc000172034>] ftrace_return_to_handler+0x11c/0x150
 > [<ffffffc0000924bc>] return_to_handler+0x1c/0x40
 > [<ffffffc0000924a0>] return_to_handler+0x0/0x40
 > [<ffffffc0000924a0>] return_to_handler+0x0/0x40
 > [<ffffffc0000924a0>] return_to_handler+0x0/0x40
 > [<ffffffc0000924a0>] return_to_handler+0x0/0x40
 > [<ffffffc0000924a0>] return_to_handler+0x0/0x40
 > [<ffffffc0000924a0>] return_to_handler+0x0/0x40

These call stacks were:
   (psci_cpu_suspend)
   psci_suspend_finisher
   (cpu_suspend_enter?)
   cpu_suspend
   cpu_psci_cpu_suspend
   arm_cpuidle_suspend
   arm_enter_idle_state
   cpuidle_enter_state
   cpuidle_enter
   call_cpuidle
   (cpu_startup_entry?)

and if cpuidle is turned off(cpuidle.off=1), the panic never happens.
That is all what I know at this moment.

-Takahiro AKASHI

 > [<ffffffc000090208>] secondary_start_kernel+0x130/0x158
 > Unable to handle kernel NULL pointer dereference at virtual address 00000000
 > pgd = ffffffc000b68000
 > [00000000] *pgd=00000009f69ea003, *pud=00000009f69ea003, *pmd=00000009f69eb003, *pte=006000002c010707
 > Internal error: Oops: 96000006 [#1] PREEMPT SMP
   [snip]

On 11/12/2015 07:42 PM, Catalin Marinas wrote:
> Hi Takahiro,
>
> I was trying to assess what's working/not working in ftrace on arm64 and
> whether your recent patches are meant for 4.4 or can wait until 4.5.
> However, without any patches applied on a 4.3 kernel, enabling the
> function_graph tracer when CONFIG_DYNAMIC_FTRACE is enabled panics the
> kernel. Strangely, it does not happen if only a single CPU is on.
> However, with function_graph tracer on, onlining a second CPU leads to a
> similar panic.
>
> Below is the kernel panic with 2 CPUs online on a Juno board. There
> isn't much stack trace information for CPU 5 where the fault happened,
> the frame pointer (x29) seems corrupted as well. Any idea? Thanks.
>
> # echo function_graph > /sys/kernel/debug/tracing/current_tracer
> swapper/5[0]: undefined instruction: pc=ffffffc000a46698
> Code: 0009ccf8 ffffffc0 00000000 00000000 (00000030)
> Internal error: Oops - undefined instruction: 0 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 5 PID: 0 Comm: swapper/5 Not tainted 4.3.0 #574
> Hardware name: Juno (DT)
> task: ffffffc976b23ac0 ti: ffffffc976b3c000 task.ti: ffffffc976b3c000
> PC is at cpu_online_bits+0x0/0x8
> LR is at cpu_online_bits+0x0/0x8
> pc : [<ffffffc000a46698>] lr : [<ffffffc000a46698>] pstate: 600001c5
> sp : ffffffc976b3ff40
> x29: 0000000000000002 x28: ffffffc000100c0c
> x27: ffffffc000aeb790 x26: ffffffc9758d5800
> x25: 0000000000000002 x24: ffffffc0000924a0
> x23: ffffffc976b3ff40 x22: ffffffc00056841c
> x21: ffffffc000a25b80 x20: ffffffc000aeb790
> x19: ffffffc9758d5800 x18: 0000000000000000
> x17: 0000000000000000 x16: 0000000000000000
> x15: 0000000000000000 x14: 0000000000000000
> x13: 0000000000000000 x12: 0000000034d5d91d
> x11: 0000000000000000 x10: 0000000000001000
> x9 : ffffffc9768070c0 x8 : 00000000000007d8
> x7 : 0000001b280eb7c4 x6 : 0000000000000015
> x5 : 000000000000000a x4 : ffffffc0792a4990
> x3 : ffffffffffffffa1 x2 : ffffffc0792a4800
> x1 : ffffffc0000949e0 x0 : ffffffffffffffa1
>
> Process swapper/5 (pid: 0, stack limit = 0xffffffc976b3c020)
> Stack: (0xffffffc976b3ff40 to 0xffffffc976b40000)
> ff40: ffffffc976b3ff70 ffffffc0000924a0 ffffffc976b3c000 ffffffc000a46000
> ff60: ffffffc000b20000 0000001b27d716c0 ffffffc976b3ffd0 ffffffc000090208
> ff80: 0000000000000005 0000000000000e12 ffffffc000b306a0 0000000000000000
> ffa0: 0000000000000000 0000000000000000 0000000080b65000 0000000080b68000
> ffc0: ffffffc0000827f0 0000000000000000 0000000000000000 00000000800827dc
> ffe0: 0000000000000000 0000000000000000 068824085611a721 280b8a0b05808446
> Call trace:
> Code: 0009ccf8 ffffffc0 00000000 00000000 (00000030)
> ---[ end trace 702bb2ed35464601 ]---
> Kernel panic - not syncing: Attempted to kill the idle task!
> CPU4: stopping
> CPU: 4 PID: 0 Comm: swapper/4 Tainted: G      D         4.3.0 #574
> Hardware name: Juno (DT)
> Call trace:
> [<ffffffc00008aaa8>] dump_backtrace+0x0/0x150
> [<ffffffc00008ac1c>] show_stack+0x24/0x30
> [<ffffffc0003b21a0>] dump_stack+0x90/0xd0
> [<ffffffc000090880>] handle_IPI+0x280/0x290
> [<ffffffc00008255c>] gic_handle_irq+0x94/0xb0
> Exception stack(0xffffffc976b3bd70 to 0xffffffc976b3be90)
> bd60:                                   0000001b2ed1ee8c ffffffc000aeb850
> bd80: ffffffc976b3bec0 ffffffc0005681dc 0000000080000145 ffffffc00009244c
> bda0: 0000000000000000 0000000000000001 ffffffc976b38000 0000000000000003
> bdc0: ffffffc976b38000 ffffffc000a282a8 ffffffc976b38000 ffffffc0000ecb28
> bde0: 00000000000006ed ffffffc9768070c0 00000000000007e0 ffffffc0006d04a8
> be00: 0000000000000001 0000000000005a0e 0000000000000001 ffffffc0006d04a8
> be20: 0000000000000000 0000000000000000 0000000000000001 0000001b2ed1ee8c
> be40: ffffffc000aeb850 ffffffc9758d5600 0000000000000000 ffffffc000aeb790
> be60: 0000000000000004 0000001b2e40a7ec ffffffc976b3bf70 ffffffc000a29f20
> be80: ffffffc0006c9000 ffffffc976b3bec0
> [<ffffffc0000855ac>] el1_irq+0x6c/0xe0
> [<ffffffc00056842c>] cpuidle_enter+0x34/0x48
> [<ffffffc000100c30>] call_cpuidle+0x48/0x80
> [<ffffffc000100e90>] cpu_startup_entry+0x228/0x308
> [<ffffffc000090208>] secondary_start_kernel+0x130/0x158
> ---[ end Kernel panic - not syncing: Attempted to kill the idle task!
>