linux-kernel - Re: [PATCH 1/3] kernel.h: drop STACK

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Message-ID: <aS5T9-1z7PK32q9R@yury>
Date: Mon, 1 Dec 2025 21:50:31 -0500
From: Yury Norov <yury.norov@...il.com>
To: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Daniel Gomez <da.gomez@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.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 1/3] kernel.h: drop STACK_MAGIC macro

On Mon, Dec 01, 2025 at 10:38:01AM +0100, Christophe Leroy (CS GROUP) wrote:
> 
> 
> Le 29/11/2025 à 20:53, Yury Norov (NVIDIA) a écrit :
> > The macro is only used by i915. Move it to a local header and drop from
> > the kernel.h.
> 
> At the begining of the git history we have:
> 
> $ git grep STACK_MAGIC 1da177e4c3f41
> 1da177e4c3f41:arch/h8300/kernel/traps.c:        if (STACK_MAGIC !=
> *(unsigned long *)((unsigned long)current+PAGE_SIZE))
> 1da177e4c3f41:arch/m68k/mac/macints.c:          if (STACK_MAGIC !=
> *(unsigned long *)current->kernel_stack_page)
> 1da177e4c3f41:include/linux/kernel.h:#define STACK_MAGIC        0xdeadbeef
> 
> Would be good to know the history of its usage over time.
> 
> I see:
> - Removed from m68k by 3cd53b14e7c4 ("m68k/mac: Improve NMI handler")
> - Removed from h8300 by 1c4b5ecb7ea1 ("remove the h8300 architecture")
> - Started being used in i915 selftest by 250f8c8140ac ("drm/i915/gtt:
> Read-only pages for insert_entries on bdw+")

STACK_MAGIC was added in 1994 in 1.0.2.  It was indeed used in a couple
of places in core subsystems back then to detect stack corruption. But
since that people invented better ways to guard stacks.

You can check commit 4914d770dec4 in this project:

https://archive.org/details/git-history-of-linux