linux-kernel - Re: [PATCH v2] printk: Add a short description string to kmsg

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Message-ID: <202407030926.D5DA9B901D@keescook>
Date: Wed, 3 Jul 2024 09:27:04 -0700
From: Kees Cook <kees@...nel.org>
To: Petr Mladek <pmladek@...e.com>
Cc: Jocelyn Falempe <jfalempe@...hat.com>,
	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>,
	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 v2] printk: Add a short description string to kmsg_dump()

On Wed, Jul 03, 2024 at 10:22:11AM +0200, Petr Mladek wrote:
> On Wed 2024-07-03 09:57:26, Jocelyn Falempe wrote:
> > 
> > 
> > On 02/07/2024 22:29, Kees Cook wrote:
> > > On Tue, Jul 02, 2024 at 02:26:04PM +0200, Jocelyn Falempe wrote:
> > > > kmsg_dump doesn't forward the panic reason string to the kmsg_dumper
> > > > callback.
> > > > This patch adds a new struct kmsg_dump_detail, that will hold the
> > > > reason and description, and pass it to the dump() callback.
> > > 
> > > Thanks! I like this much better. :)
> > > 
> > > > 
> > > > 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.
> > > > 
> > > > v2:
> > > >   * Use a struct kmsg_dump_detail to hold the reason and description
> > > >     pointer, for more flexibility if we want to add other parameters.
> > > >     (Kees Cook)
> > > >   * Fix powerpc/nvram_64 build, as I didn't update the forward
> > > >     declaration of oops_to_nvram()
> > > 
> > > The versioning history commonly goes after the "---".
> > 
> > ok, I was not aware of this.
> > > 
> > > > [...]
> > > > diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
> > > > index 906521c2329c..65f5a47727bc 100644
> > > > --- a/include/linux/kmsg_dump.h
> > > > +++ b/include/linux/kmsg_dump.h
> > > > @@ -39,6 +39,17 @@ struct kmsg_dump_iter {
> > > >   	u64	next_seq;
> > > >   };
> > > > +/**
> > > > + *struct kmsg_dump_detail - kernel crash detail
> > > 
> > > Is kern-doc happy with this? I think there is supposed to be a space
> > > between the "*" and the first word:
> > > 
> > >   /**
> > >    * struct kmsg...
> > > 
> > > 
> > Good catch, yes there is a space missing.
> > 
> > I just checked with "make htmldocs", and in fact include/linux/kmsg_dump.h
> > is not indexed for kernel documentation.
> > And you can't find the definition of struct kmsg_dumper in the online doc.
> > https://www.kernel.org/doc/html/latest/search.html?q=kmsg_dumper
> > 
> > > Otherwise looks good to me!
> > > 
> > 
> > Thanks.
> > 
> > As this patch touches different subsystems, do you know on which tree it
> > should land ?
> 
> Andrew usually takes patches against kernel/panic.c.
> 
> Or you could take it via the DRM tree, especially if you already have the code
> using the string.
> 
> Also I could take it via the printk tree. The only complication is
> that I am going to be away the following two weeks and would come
> back in the middle of the merge window. I do not expect much problems
> with this change but...

If DRM doesn't want to carry it, I can put it in through the pstore
tree. Let me know! :)

-- 
Kees Cook