linux-kernel - Re: [PATCH v2] earlycon: prevent multiple register

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Date:   Thu, 2 Jun 2022 09:29:59 -0500
From:   Rob Herring <robh@...nel.org>
To:     Michael Walle <michael@...le.cc>
Cc:     Frank Rowand <frowand.list@...il.com>,
        linux-serial@...r.kernel.org, Jiri Slaby <jirislaby@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2] earlycon: prevent multiple register_console()

On Thu, 02 Jun 2022 11:00:38 +0200, Michael Walle wrote:
> If the earlycon parameter is given twice, the kernel will spit out a
> WARN() in register_console() because it was already registered. The
> non-dt variant setup_earlycon() already handles that gracefully. The dt
> variant of_setup_earlycon() doesn't. Add the check there and add the
> -EALREADY handling in early_init_dt_scan_chosen_stdout().
> 
> FWIW, this doesn't happen if CONFIG_ACPI_SPCR_TABLE is set. In that case
> the registration is delayed until after earlycon parameter(s) are
> parsed.
> 
> Signed-off-by: Michael Walle <michael@...le.cc>
> ---
> changes since v1:
>  - add missing EALREADY handling in of_setup_earlycon()
>  - return 0 early as suggested by Rob
> 
> For the curious, here is the backtrace:
> 
> [    0.000000] ------------[ cut here ]------------
> [    0.000000] WARNING: CPU: 0 PID: 0 at kernel/printk/printk.c:3328 register_console+0x2b4/0x364
> [    0.000000] console 'atmel_serial0' already registered
> [    0.000000] Modules linked in:
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.18.0-next-20220601+ #652
> [    0.000000] Hardware name: Generic DT based system
> [    0.000000] Backtrace:
> [    0.000000]  dump_backtrace from show_stack+0x18/0x1c
> [    0.000000]  show_stack from dump_stack_lvl+0x48/0x54
> [    0.000000]  dump_stack_lvl from dump_stack+0x18/0x1c
> [    0.000000]  dump_stack from __warn+0xd0/0x148
> [    0.000000]  __warn from warn_slowpath_fmt+0x9c/0xc4
> [    0.000000]  warn_slowpath_fmt from register_console+0x2b4/0x364
> [    0.000000]  register_console from of_setup_earlycon+0x29c/0x2ac
> [    0.000000]  of_setup_earlycon from early_init_dt_scan_chosen_stdout+0x154/0x18c
> [    0.000000]  early_init_dt_scan_chosen_stdout from param_setup_earlycon+0x40/0x48
> [    0.000000]  param_setup_earlycon from do_early_param+0x88/0xc4
> [    0.000000]  do_early_param from parse_args+0x1a4/0x404
> [    0.000000]  parse_args from parse_early_options+0x40/0x48
> [    0.000000]  parse_early_options from parse_early_param+0x38/0x48
> [    0.000000]  parse_early_param from setup_arch+0x114/0x7a4
> [    0.000000]  setup_arch from start_kernel+0x74/0x6dc
> [    0.000000]  start_kernel from 0x0
> [    0.000000] ---[ end trace 0000000000000000 ]---
> 
>  drivers/of/fdt.c              | 4 +++-
>  drivers/tty/serial/earlycon.c | 3 +++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 

Reviewed-by: Rob Herring <robh@...nel.org>