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Message-ID: <1d0e141c-1afe-4646-8e6f-584e2a0706e2@yoseli.org>
Date: Mon, 2 Dec 2024 18:53:25 +0100
From: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
To: Greg Ungerer <gerg@...ux-m68k.org>, linux-m68k@...ts.linux-m68k.org
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
rostedt@...dmis.org, Michael Schmitz <schmitzmic@...il.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH RFC 2/2] arch: m68k: Add STACKTRACE support
Hi Greg,
On 02/12/2024 15:41, Greg Ungerer wrote:
> Hi JM,
>
> On 27/11/24 21:26, Jean-Michel Hautbois wrote:
>> Hi there,
>>
>> On 21/10/2024 11:44, Jean-Michel Hautbois wrote:
>>> In order to use tracing, implement a basic arch_stack_walk() based on
>>> the one in PowerPC.
>>> Tested on a M54418 coldfire.
>>
>> Well, I said it was tested, but it was only compile tested basically.
>> AFAICT now, I think it is not working as when I use wakeup_rt as a
>> tracer, I don't have the stack trace:
>>
>> # wakeup_rt latency trace v1.1.5 on 6.12.0-10380-gb66f06337b66-dirty
>> # --------------------------------------------------------------------
>> # latency: 2000 us, #18/18, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0)
>> # -----------------
>> # | task: irq/100-enet-fe-118 (uid:0 nice:0 policy:1 rt_prio:50)
>> # -----------------
>> #
>> # _------=> CPU#
>> # / _-----=> irqs-off/BH-disabled
>> # | / _----=> need-resched
>> # || / _---=> hardirq/softirq
>> # ||| / _--=> preempt-depth
>> # |||| / _-=> migrate-disable
>> # ||||| / delay
>> # cmd pid |||||| time | caller
>> # \ / |||||| \ | /
>> kworker/-11 0dnh5. 0us : 11:120:R + [000] 22:
>> 98:R irq_work/0
>> kworker/-11 0dnh5. 0us : <stack trace>
>> kworker/-11 0dnh5. 0us : 0
>> kworker/-11 0d..3. 0us : __schedule
>> kworker/-11 0d..3. 0us : 11:120:R ==> [000] 22:
>> 98:R irq_work/0
>> kworker/-11 0d..3. 0us : <stack trace>
>> telnetd-229 0Dnh4. 0us : 229:120:R + [000] 118:
>> 49:R irq/100-enet-fe
>> telnetd-229 0Dnh4. 0us : <stack trace>
>> telnetd-229 0Dnh4. 0us : 0
>> telnetd-229 0D..3. 0us : __schedule
>> telnetd-229 0D..3. 0us : 229:120:R ==> [000] 118:
>> 49:R irq/100-enet-fe
>> telnetd-229 0D..3. 0us : <stack trace>
>> telnetd-229 0dn.5. 0us : 229:120:R + [000] 118:
>> 49:R irq/100-enet-fe
>> telnetd-229 0dn.5. 0us : <stack trace>
>> telnetd-229 0dn.5. 0us#: 0
>> telnetd-229 0d..3. 2000us : __schedule
>> telnetd-229 0d..3. 2000us : 229:120:R ==> [000] 118:
>> 49:R irq/100-enet-fe
>> telnetd-229 0d..3. 2000us : <stack trace>
>>
>> Geert, Greg, and maybe other highly skilled m68k people, could you
>> please help me with this particular function :-) ?
>>
>> Thanks !
>> JM
>>
>>>
>>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
>>> ---
>>> arch/m68k/Kconfig | 5 ++++
>>> arch/m68k/kernel/Makefile | 1 +
>>> arch/m68k/kernel/stacktrace.c | 70 ++++++++++++++++++++++++++++++++
>>> +++++++++++
>>> 3 files changed, 76 insertions(+)
>>>
>>> diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
>>> index
>>> ab3375475721fa63418c40d4ba6ac76679ebc77d..7142f9759181a90269ae1ba9e682d331ee2ddbf6 100644
>>> --- a/arch/m68k/Kconfig
>>> +++ b/arch/m68k/Kconfig
>>> @@ -40,6 +40,7 @@ config M68K
>>> select UACCESS_MEMCPY if !MMU
>>> select ZONE_DMA
>>> select TRACE_IRQFLAGS_SUPPORT
>>> + select ARCH_STACKWALK
>>> config CPU_BIG_ENDIAN
>>> def_bool y
>>> @@ -107,6 +108,10 @@ config BOOTINFO_PROC
>>> Say Y to export the bootinfo used to boot the kernel in a
>>> "bootinfo" file in procfs. This is useful with kexec.
>>> +config STACKTRACE_SUPPORT
>>> + bool
>>> + default y
>>> +
>>> menu "Platform setup"
>>> source "arch/m68k/Kconfig.cpu"
>>> diff --git a/arch/m68k/kernel/Makefile b/arch/m68k/kernel/Makefile
>>> index
>>> f335bf3268a108a45bab079fbf0a1c8ead9beb71..4efe92af0b711b19cb1d5129f74e67a739e289b1 100644
>>> --- a/arch/m68k/kernel/Makefile
>>> +++ b/arch/m68k/kernel/Makefile
>>> @@ -31,3 +31,4 @@ obj-$(CONFIG_UBOOT) += uboot.o
>>> obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
>>> +obj-y += stacktrace.o
>>> diff --git a/arch/m68k/kernel/stacktrace.c b/arch/m68k/kernel/
>>> stacktrace.c
>>> new file mode 100644
>>> index
>>> 0000000000000000000000000000000000000000..06c7459373bd25b3bb3540cfe2a909259c1db3ce
>>> --- /dev/null
>>> +++ b/arch/m68k/kernel/stacktrace.c
>>> @@ -0,0 +1,70 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +
>>> +/*
>>> + * Stack trace utility functions etc.
>>> + *
>>> + * Copyright 2024 Jean-Michel Hautbois, Yoseli SAS.
>>> + */
>>> +
>>> +#include <asm/current.h>
>>> +#include <asm/ptrace.h>
>>> +#include <linux/sched.h>
>>> +#include <linux/sched/task_stack.h>
>>> +#include <linux/stacktrace.h>
>>> +
>>> +static inline unsigned long current_stack_frame(void)
>>> +{
>>> + unsigned long sp;
>>> +
>>> + asm volatile("movl %%sp, %0" : "=r"(sp));
>>> + return sp;
>>> +}
>
> If I am understanding what this is intended to do then this is probably
> not right.
> This will be returning the current stack pointer, which will almost
> certainly not
> be the current stack frame pointer. This will be the top of stack at the
> call site,
> which will be after the pushed locals and saved registers at the very
> least for m68k.
>
> Does your kernel config have CONFIG_FRAME_POINTER enabled?
> The default for m68k is usually disabled. Without this there won't be a
> chain of frame pointers to follow like the code is trying to do below in
> arch_stack_walk().
>
It gives me a few things when I use wakeup_rt but timerlat is not giving
me any stack:
# cd /sys/kernel/debug/tracing/
# echo 500 > osnoise/stop_tracing_total_us
# echo 500 > osnoise/print_stack
# echo timerlat > current_tracer
# echo 1 > tracing_on
# tail -21 trace
# tail -21 trace
timerlat/0-299 [000] ..... 635.167643: #59035 context
thread timer_latency 202352 ns
kworker/u5:1-242 [000] d.h1. 635.168494: #59036 context
irq timer_latency 51504 ns
timerlat/0-299 [000] ..... 635.168714: #59036 context
thread timer_latency 272032 ns
bash-230 [000] d.h.. 635.169496: #59037 context
irq timer_latency 54592 ns
timerlat/0-299 [000] ..... 635.169693: #59037 context
thread timer_latency 250448 ns
bash-230 [000] d.h.. 635.170491: #59038 context
irq timer_latency 48784 ns
timerlat/0-299 [000] ..... 635.170717: #59038 context
thread timer_latency 275960 ns
bash-230 [000] d.h.. 635.171497: #59039 context
irq timer_latency 54472 ns
timerlat/0-299 [000] ..... 635.171695: #59039 context
thread timer_latency 252936 ns
bash-230 [000] d.h1. 635.172495: #59040 context
irq timer_latency 53064 ns
timerlat/0-299 [000] ..... 635.172696: #59040 context
thread timer_latency 253144 ns
bash-230 [000] d.h1. 635.173491: #59041 context
irq timer_latency 49864 ns
timerlat/0-299 [000] ..... 635.173683: #59041 context
thread timer_latency 241248 ns
bash-230 [000] d.h1. 635.174495: #59042 context
irq timer_latency 52648 ns
timerlat/0-299 [000] ..... 635.174691: #59042 context
thread timer_latency 249216 ns
bash-230 [000] d.h.. 635.175536: #59043 context
irq timer_latency 94496 ns
timerlat/0-299 [000] ..... 635.175762: #59043 context
thread timer_latency 321592 ns
bash-324 [000] d.h.. 635.176825: #59044 context
irq timer_latency 383560 ns
timerlat/0-299 [000] ..... 635.177044: #59044 context
thread timer_latency 603280 ns
timerlat/0-299 [000] ...1. 635.177091: <stack trace>
timerlat/0-299 [000] ..... 635.177141: timerlat_main: stop
tracing hit on cpu 0
As you can see, stack_trace appears, but nothing is displayed so I
suppose it does not walk at all...
Thanks,
JM
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