linux-kernel - Re: [PATCH v8 10/12] unwind_user/sframe: Enable debugging in uaccess regions

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Message-ID: <CAHk-=widGT2M=kJJr6TwWsMjfYSghL9k3LgxJvRard0wtiP62A@mail.gmail.com>
Date: Mon, 7 Jul 2025 20:38:35 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Steven Rostedt <rostedt@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	bpf@...r.kernel.org, x86@...nel.org, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 
	Namhyung Kim <namhyung@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Andrii Nakryiko <andrii@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>, 
	"Jose E. Marchesi" <jemarch@....org>, Beau Belgrave <beaub@...ux.microsoft.com>, 
	Jens Remus <jremus@...ux.ibm.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Jens Axboe <axboe@...nel.dk>, Florian Weimer <fweimer@...hat.com>, Sam James <sam@...too.org>
Subject: Re: [PATCH v8 10/12] unwind_user/sframe: Enable debugging in uaccess regions

On Mon, 7 Jul 2025 at 19:12, Steven Rostedt <rostedt@...nel.org> wrote:
>
> From: Josh Poimboeuf <jpoimboe@...nel.org>
>
> Objtool warns about calling pr_debug() from uaccess-enabled regions, and
> rightfully so.  Add a dbg_sec_uaccess() macro which temporarily disables
> uaccess before doing the dynamic printk, and use that to add debug
> messages throughout the uaccess-enabled regions.

Please kill this patch, and stop doing stupid things.

The whole AND ONLY point of using the unsafe user access macros is
performance. You are now actively breaking the whole point of them.

If you need to add debug printouts to user accesses, just don't use
the 'unsafe' ones.

Or add the debug to after the unsafe region has finished. Not this way.

This patch is disgusting, in other words. It's wrong. STOP IT.

              Linus