linux-kernel - Re: [PATCH v10 04/14] unwind_user/deferred: Add unwind_deferred

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Message-ID: <20250619075417.GW1613376@noisy.programming.kicks-ass.net>
Date: Thu, 19 Jun 2025 09:54:17 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.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>,
	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>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v10 04/14] unwind_user/deferred: Add
 unwind_deferred_trace()

On Wed, Jun 18, 2025 at 11:29:39AM -0400, Steven Rostedt wrote:

> Note, a request from the gcc folks is to add a system call that gives the
> user space application a backtrace from its current location. This can be
> handy for debugging as it would be similar to how we use dump_stack().

That makes very little sense to me; apps can typically unwind themselves
just fine, no? In fact, they can use DWARFs and all that.

Also, how about we don't make thing complicated and not confuse comments
with things like this? Focus on the deferred stuff (that's what these
patches are about) -- and then return-to-user is the one and only place
that makes sense.