linux-kernel - Re: Panic on ppc64le using kernel 5.13.0-rc3

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Message-ID: <4434f245-db3b-c02a-36c4-0111a0dfb78d@rasmusvillemoes.dk>
Date:   Fri, 11 Jun 2021 23:49:06 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Bruno Goncalves <bgoncalv@...hat.com>
Cc:     linux-kernel@...r.kernel.org, CKI Project <cki-project@...hat.com>
Subject: Re: Panic on ppc64le using kernel 5.13.0-rc3

On 11/06/2021 17.06, Bruno Goncalves wrote:
> On Fri, Jun 11, 2021 at 9:13 AM Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
>>
>> On 10/06/2021 17.14, Bruno Goncalves wrote:
>>> On Thu, Jun 10, 2021 at 3:02 PM Rasmus Villemoes
>>> <linux@...musvillemoes.dk> wrote:
>>>>
>>>> On 10/06/2021 13.47, Bruno Goncalves wrote:
>>>>> Hello,
>>>>>
>>>>> We've observed in some cases kernel panic when trying to boot on
>>>>> ppc64le using a kernel based on 5.13.0-rc3. We are not sure if it
>>>>> could be related to patch
>>>>> https://lore.kernel.org/lkml/20210313212528.2956377-2-linux@rasmusvillemoes.dk/
>>>>>
>>>>
>>>> Thanks for the report. It's possible, but I'll need some help from you
>>>> to get more info.
>>>>
>>>> First, can you send me the .config?
>>>
>>> The .config is on
>>> https://s3.us-east-1.amazonaws.com/arr-cki-prod-datawarehouse-public/datawarehouse-public/2021/06/09/317881801/build_ppc64le_redhat:1332368174/kernel-block-ppc64le-d3f02e52f5548006f04358d407bbb7fe51255c41.config
>>
>> Thanks.
>>
>>>>
>>>>>
>>>>> [    1.516075] wait_for_initramfs() called before rootfs_initcalls
>>>>
>>>> This is likely because you have CONFIG_UEVENT_HELPER_PATH set to some
>>>> non-empty path (/sbin/hotplug perhaps). This did get reported once before:
>>>>
>>>
>>> CONFIG_UEVENT_HELPER_PATH is not set. In the .config we have "#
>>> CONFIG_UEVENT_HELPER is not set"
>>
>> OK. Then I assume some quite early initcall does a request_module() or
>> request_firmware() (or similar). I don't think this matters - that call
>> would be done before the initramfs was unpacked with or without my
>> patch, so it won't find anything in the empty rootfs. It's just my patch
>> added a note. But just to figure out where that triggers, can you do
>>
>> -               pr_warn_once("wait_for_initramfs() called before
>> rootfs_initcalls\n");
>> +               WARN_ONCE(1, "wait_for_initramfs() called before
>> rootfs_initcalls\n");
>>
>> in init/initramfs.c.
>>
> 
> I've managed to reproduce the panic with the patch.
> 
> [    1.498654] NIP [c0000000000137d4] wait_for_initramfs+0x94/0xa4
> [    1.498661] LR [c0000000000137d0] wait_for_initramfs+0x90/0xa4
> [    1.498668] Call Trace:
> [    1.498671] [c000000027debd60] [c0000000000137d0]
> wait_for_initramfs+0x90/0xa4 (unreliable)
> [    1.498680] [c000000027debdc0] [c000000000172fc8]
> call_usermodehelper_exec_async+0x178/0x2c0
> [    1.498691] [c000000027debe10] [c00000000000d6ec]
> ret_from_kernel_thread+0x5c/0x70

Thanks, but unfortunately (and I should have known better) that doesn't
tell us who actually initated that call_usermodehelper - it's most
likely some request_module() call. But again, I don't think this is
related to the later crash.

>>>>> [    1.764430] Initramfs unpacking failed: no cpio magic
>>>>
>>>> Whoa, that's not good. Did something scramble over the initramfs memory
>>>> while it was being unpacked? It's been .2 seconds since the start of the
>>>> unpacking, so it's unlikely the very beginning of the initramfs is corrupt.
>>>>
>>>> Can you try booting with initramfs_async=0 on the command line and see
>>>> if the kernel still crashes?
> 
> Using initramfs_async=0 I was also able to reproduce the panic.

Hm, that's very interesting. Can you share the log for that as well?

And, perhaps asking a silly question, does the crash go away if you
revert e7cb072eb988e46295512617c39d004f9e1c26f8 ?

Thanks,
Rasmus