linux-kernel - Re: [PATCH] printk: Add a short description string to kmsg

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Date: Wed, 26 Jun 2024 10:00:23 +0200
From: Petr Mladek <pmladek@...e.com>
To: Jocelyn Falempe <jfalempe@...hat.com>
Cc: Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Richard Weinberger <richard@....at>,
	Vignesh Raghavendra <vigneshr@...com>, Kees Cook <kees@...nel.org>,
	Tony Luck <tony.luck@...el.com>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jani Nikula <jani.nikula@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Uros Bizjak <ubizjak@...il.com>, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-hyperv@...r.kernel.org, linux-mtd@...ts.infradead.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] printk: Add a short description string to kmsg_dump()

On Tue 2024-06-25 14:39:29, Jocelyn Falempe wrote:
> kmsg_dump doesn't forward the panic reason string to the kmsg_dumper
> callback.
> This patch adds a new parameter "const char *desc" to the kmsg_dumper
> dump() callback, and update all drivers that are using it.
> 
> To avoid updating all kmsg_dump() call, it adds a kmsg_dump_desc()
> function and a macro for backward compatibility.
> 
> I've written this for drm_panic, but it can be useful for other
> kmsg_dumper.
> It allows to see the panic reason, like "sysrq triggered crash"
> or "VFS: Unable to mount root fs on xxxx" on the drm panic screen.
>
> Signed-off-by: Jocelyn Falempe <jfalempe@...hat.com>
> ---
>  arch/powerpc/kernel/nvram_64.c             |  3 ++-
>  arch/powerpc/platforms/powernv/opal-kmsg.c |  3 ++-
>  drivers/gpu/drm/drm_panic.c                |  3 ++-
>  drivers/hv/hv_common.c                     |  3 ++-
>  drivers/mtd/mtdoops.c                      |  3 ++-
>  fs/pstore/platform.c                       |  3 ++-
>  include/linux/kmsg_dump.h                  | 13 ++++++++++---
>  kernel/panic.c                             |  2 +-
>  kernel/printk/printk.c                     |  8 +++++---
>  9 files changed, 28 insertions(+), 13 deletions(-)

The parameter is added into all dumpers. I guess that it would be
used only drm_panic() because it is graphics and might be "fancy".
The others simply dump the log buffer and the reason is in
the dumped log as well.

Anyway, the passed buffer is static. Alternative solution would
be to make it global and export it like, for example, panic_cpu.

Best Regards,
Petr