linux-kernel - Re: [PATCH v4 7/7] kernel.h: drop trace

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Message-ID: <aVvoe5fQN3EUtEAJ@yury>
Date: Mon, 5 Jan 2026 11:36:11 -0500
From: Yury Norov <yury.norov@...il.com>
To: Jani Nikula <jani.nikula@...ux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Christophe Leroy <chleroy@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	David Laight <david.laight@...box.com>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Andi Shyti <andi.shyti@...nel.org>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	Daniel Gomez <da.gomez@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>, linux-kernel@...r.kernel.org,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-modules@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v4 7/7] kernel.h: drop trace_printk.h

On Mon, Jan 05, 2026 at 11:29:51AM +0200, Jani Nikula wrote:
> On Sat, 03 Jan 2026, Yury Norov <yury.norov@...il.com> wrote:
> > On Sat, Jan 03, 2026 at 02:57:58PM +0200, Andy Shevchenko wrote:
> >> On Fri, Jan 02, 2026 at 07:50:59PM -0500, Joel Fernandes wrote:
> >> > On Mon, Dec 29, 2025 at 11:17:48AM -0500, Steven Rostedt wrote:
> >> 
> >> ...
> >> 
> >> > I use trace_printk() all the time for kernel, particularly RCU development.
> >> > One of the key usecases I have is dumping traces on panic (with panic on warn
> >> > and stop tracing on warn enabled). This is extremely useful since I can add
> >> > custom tracing and dump traces when rare conditions occur. I fixed several
> >> > bugs with this technique.
> >> > 
> >> > I also recommend keeping it convenient to use.
> >> 
> >> Okay, you know C, please share your opinion what header is the best to hold the
> >> trace_printk.h to be included.
> >
> > What if we include it on Makefile level, similarly to how W=1 works?
> >
> >         make D=1 // trace_printk() is available
> >         make D=0 // trace_printk() is not available
> >         make     // trace_printk() is not available
> >
> > Where D stands for debugging.
> >
> > D=1 may be a default setting if you prefer, but the most important is
> > that every compilation unit will have an access to debugging without
> > polluting core headers.
> 
> You do realize this means recompiling everything when adding D=1 for
> debugging?

Yes sir I do.

It would be as simple (or hard) as building another arch:

        make O=../build/linux-arm64
        make O=../build/linux-x86_64
        make D=1 W=1 O=../build/linux-x86_64-dev

If you're both developer and CI engineer in your company, you're likely
already doing something like that. If you're CI-only, there're no
changes for you. If you're a developer - yeah, you'd have to learn a
new flag.

The real problem of course is the status inflation. The fact that
defconfig enables CONFIG_EXPERT and CONFIG_DEBUG_KERNEL implies that
every random person who is able to do:

        git clone && make && sudo make install

now assumed an expert kernel user and active developer. It is not
correct, and it leads to bloating kernel with dev-only features.

What we discuss here is a new marker for those real experts and
developers, I think. (In an hope that it will inflate not very fast.)

Thanks,
Yury