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

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Message-ID: <4aa3a028-04e5-4658-9879-df60dab06c54@redhat.com>
Date: Thu, 27 Jun 2024 09:29:25 +0200
From: Jocelyn Falempe <jfalempe@...hat.com>
To: Petr Mladek <pmladek@...e.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 26/06/2024 10:00, Petr Mladek wrote:
> 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.

Ok, I also tried to retrieve the reason from the dumped log, but that's 
really fragile.

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

It's not a static buffer, because the string is generated at runtime.
eg: https://elixir.bootlin.com/linux/latest/source/arch/arm/mm/init.c#L158

So it will be hard to avoid race conditions.

> 
> Best Regards,
> Petr
>