linux-kernel - Re: [PATCH 43/50] xtensa: Add show_stack

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Message-ID: <836351a4-581d-325f-862f-99c0c4f98e19@arista.com>
Date:   Wed, 6 Nov 2019 16:06:44 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     Petr Mladek <pmladek@...e.com>, Max Filippov <jcmvbkbc@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Chris Zankel <chris@...kel.net>,
        "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>
Subject: Re: [PATCH 43/50] xtensa: Add show_stack_loglvl()

On 11/6/19 8:15 AM, Petr Mladek wrote:
> On Tue 2019-11-05 20:13:22, Max Filippov wrote:
[..]
>>> @@ -511,16 +512,21 @@ void show_stack(struct task_struct *task, unsigned long *sp)
>>>                 sp = stack_pointer(task);
>>>         stack = sp;
>>>
>>> -       pr_info("Stack:\n");
>>> +       printk("%sStack:\n", loglvl);
>>>
>>>         for (i = 0; i < kstack_depth_to_print; i++) {
>>>                 if (kstack_end(sp))
>>>                         break;
>>> -               pr_cont(" %08lx", *sp++);
>>> +               printk("%s %08lx", loglvl, *sp++);
> 
> KERN_CONT can be combined with any other loglevel.
> So you could keep using pr_cont() together with explicit loglevel:
> 
> 			pr_cont("%s %08lx", loglvl, *sp++);

Yes, that's what I had, but than misread the printk() code and thought
that it doesn't add '\n' to messages.. Will fix.

> It should fix the problems reported below.
> 
> Well, the preferred solution would be to snprintf() the continuous
> line into a temporary buffer. And printk() it when it is complete.
> pr_cont() is not reliable when more CPUs print at the same time.

Yep. Not sure if doing it now in those per-arch patches or keep the
changes to minimum.

> 
>> This change doesn't work well with printk timestamps, it changes
>> the following output on xtensa architecture
>>
>> [    3.404675] Stack:
>> [    3.404861]  a05773e2 00000018 bb03dc34 bb03dc30 a0008640 bb03dc70
>> ba9ba410 37c3f000
>> [    3.405414]  37c3f000 d7c3f000 00000800 bb03dc50 a02b97ed bb03dc90
>> ba9ba400 ba9ba410
>> [    3.405969]  a05fc1bc bbff28dc 00000000 bb03dc70 a02b7fb9 bb03dce0
>> ba9ba410 a0579044
>>
>> into this:
>> [    3.056825] Stack:
>> [    3.056963]  a04ebb20
>> [    3.056995]  bb03dc10
>> [    3.057138]  00000001
>> [    3.057277]  bb03dc10
>> [    3.057815]  a00083ca
>> [    3.057965]  bb03dc50
>> [    3.058107]  ba9ba410
>> [    3.058247]  37c3f000
>> [    3.058387]
>> [    3.058584]  a05773e2
>> [    3.058614]  00000001
>> [    3.058755]  a05ca0bc
>> [    3.058896]  bb03dc30
>> [    3.059035]  a000865c
>> [    3.059180]  bb03dc70
>> [    3.059319]  ba9ba410
>> [    3.059459]  37c3f000
>> [    3.059598]
>> [    3.059795]  37c3f000
>> [    3.059824]  d7c3f000
>> [    3.059964]  00000800
>> [    3.060103]  bb03dc50
>> [    3.060241]  a02b9809
>> [    3.060379]  bb03dc90
>> [    3.060519]  ba9ba400
>> [    3.060658]  ba9ba410
>> [    3.060796]

Hey Max,

thanks for the testing and the report - will fix it in v2.

Thanks,
          Dmitry