Re: [PATCH] printk: Add a short description string to kmsg_dump()

From: Jocelyn Falempe <jfalempe@redhat.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
	Nicholas Piggin <npiggin@gmail.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Kees Cook <kees@kernel.org>, Tony Luck <tony.luck@intel.com>,
	"Guilherme G. Piccoli" <gpiccoli@igalia.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	John Ogness <john.ogness@linutronix.de>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jani Nikula <jani.nikula@intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Uros Bizjak <ubizjak@gmail.com>,
	linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linux-hyperv@vger.kernel.org,
	linux-mtd@lists.infradead.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] printk: Add a short description string to kmsg_dump()
Date: Thu, 27 Jun 2024 09:29:25 +0200	[thread overview]
Message-ID: <4aa3a028-04e5-4658-9879-df60dab06c54@redhat.com> (raw)
In-Reply-To: <ZnvKcnC9ruaIHYij@pathway.suse.cz>

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@redhat.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
> 