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From: Tetsuo Handa <>
To: Dmitry Vyukov <>
Cc: Guilherme Piccoli <>,
	LKML <>,
	syzkaller <>,, CKI Project <>,
	kbuild test robot <>,
Subject: Re: [PATCH V3] kernel/hung_task.c: Introduce sysctl to print all traces when a hung task is detected
Date: Mon, 30 Mar 2020 20:57:56 +0900
Message-ID: <> (raw)
In-Reply-To: <>

On 2020/03/30 18:01, Dmitry Vyukov wrote:
> On Mon, Mar 30, 2020 at 10:49 AM Dmitry Vyukov <> wrote:
>> On Mon, Mar 30, 2020 at 2:43 AM Guilherme Piccoli
>> <> wrote:
>>> Hi Tetsuo and Dmitry, thanks for noticing this Tetsuo. And sorry for
>>> not looping you in the patch Dmitry, I wasn't aware that you were
>>> working with testing. By the way, I suggest people interested in linux
>>> testing to create a ML; I'd be glad to have looped such list, but I
>>> couldn't find information about a group dealing with testing.
>>> So Tetsuo, you got it right: just change it to
>>> "sysctl.kernel.hung_task_all_cpu_backtrace=1" and that should work
>>> fine, once Vlastimil's patch gets merged (and I hope it happens soon).
>>> Cheers,
>>> Guilherme
>> +LKML, workflows, syzkaller, kernelci, cki, kbuild
>> Tetsuo, thanks for notifying again.
>> Yes, kernel devs breaking all testing happens from time to time and
>> currently there is no good way to address this.
>> Other things I remember is the introduction of CONFIG_DEBUG_MEMORY,
>> which defaults to =n and disables KASAN, which in turn produced an
>> explosion of assorted crashes caused by memory corruptions; also
>> periodic changes in kernel crash messages which I assume all testing
>> systems parse and need to understand.
>> Is there already a mailing list for this? Or should we create one?
>> I.e. announce and changes that may need actions from all testing
>> systems.

I think we can create one.

>> Another thing that may benefit from announcements is addition of new
>> useful debugging configs. Currently they are introduced silently and
>> don't reach the target audience.
> I've fixed this up:

Excuse me, but that commit is incorrect.
There will be no /proc/sys/sysctl/kernel/hung_task_all_cpu_backtrace file.
What Vlastimil's patch will allow is to set sysctl values via kernel command
line option using "sysctl." as a prefix. That is,


on dashboard/config/*.cmdline files is what you need.

> But what would be even better is some kind of canned configs/settings
> for testing systems so that I enable it once and then such changes
> magically auto-happen for me.

Yes, updating kernel config is a burden for kernel testing projects.
I'm waiting for comments from more kernel testing projects on .

> Imposing work on N testing systems maintainers is not good.
> And there really is no good point in the current kernel dev process
> for this. Announcing unmerged changes is too early (as this patch
> showed). And once it's in linux-next it's already too late..
> And I don't want to be inventing a new unique kernel configuration for
> testing. I don't think it's the right way to approach this. Whatever
> is "the testing configuration", whatever kernel developers want to see
> in task hang reports, I just want the system to provide that.

      reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
     [not found] ` <>
     [not found]   ` <>
2020-03-30  8:49     ` Dmitry Vyukov
2020-03-30  9:01       ` Dmitry Vyukov
2020-03-30 11:57         ` Tetsuo Handa [this message]

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