linux-kernel - Re: [PATCH printk v5 1/1] printk: extend console

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Message-ID: <87pmktm2a9.fsf@jogness.linutronix.de>
Date:   Wed, 04 May 2022 23:17:10 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-amlogic@...ts.infradead.org
Subject: Re: [PATCH printk v5 1/1] printk: extend console_lock for
 per-console locking

On 2022-05-03, Marek Szyprowski <m.szyprowski@...sung.com> wrote:
> QEMU virt/arm64:
>
> [  174.155760] task:pr/ttyAMA0      state:S stack:    0 pid:   26 
> ppid:     2 flags:0x00000008
> [  174.156305] Call trace:
> [  174.156529]  __switch_to+0xe8/0x160
> [  174.157131]  0xffff5ebbbfdd62d8

I can reproduce the apparent stack corruption with qemu:

[    5.545268] task:pr/ttyAMA0      state:S stack:    0 pid:   26 ppid:     2 flags:0x00000008
[    5.545520] Call trace:
[    5.545620]  __switch_to+0x104/0x160
[    5.545796]  __schedule+0x2f4/0x9f0
[    5.546122]  schedule+0x54/0xd0
[    5.546206]  0x0

When it happens, the printk-kthread is the only one with the corrupted
stack. It seems I am doing something wrong when creating the kthread? I
will investigate this.

Thanks Marek for helping us to narrow this down.

John