linux-kernel - Re: [PATCH v6 11/18] perf: Use current->flags & PF

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Message-ID: <20250425133416.63d3e3b8@gandalf.local.home>
Date: Fri, 25 Apr 2025 13:34:16 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Masami
 Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, x86@...nel.org, Peter Zijlstra
 <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Arnaldo Carvalho de
 Melo <acme@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>, Alexander
 Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa
 <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Ian Rogers
 <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>,
 linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
 linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>, Sam
 James <sam@...too.org>, Andrii Nakryiko <andrii.nakryiko@...il.com>, Jens
 Remus <jremus@...ux.ibm.com>, Florian Weimer <fweimer@...hat.com>, Andy
 Lutomirski <luto@...nel.org>, Weinan Liu <wnliu@...gle.com>, Blake Jones
 <blakejones@...gle.com>, Beau Belgrave <beaub@...ux.microsoft.com>, "Jose
 E. Marchesi" <jemarch@....org>, Alexander Aring <aahringo@...hat.com>
Subject: Re: [PATCH v6 11/18] perf: Use current->flags & PF_KTHREAD instead
 of current->mm == NULL

On Fri, 25 Apr 2025 08:09:55 -0700
Josh Poimboeuf <jpoimboe@...nel.org> wrote:

> On Fri, Apr 25, 2025 at 10:54:33AM -0400, Steven Rostedt wrote:
> > From: Steven Rostedt <rostedt@...dmis.org>
> > 
> > To determine if a task is a kernel thread or not, it is more reliable to
> > use (current->flags & PF_KTHREAD) than to rely on current->mm being NULL.
> > That is because some kernel tasks (io_uring helpers) may have a mm field.  
> 
> There's a current->mm check in the user space unwinder (patch 1) which
> should probably also be converted.

Bah! OK.

I also plan on creating a couple of macros and running a coccinelle script
to replace all instances in the kernel of:

  !(task->flags & PF_KTHREAD) into is_user_thread(task)

and

  (task->flags & PF_KTHREAD) into is_kernel_thread(task)

As I've already screwed up missing the '!' (or adding it) a couple of
times. But caught it before posting the patches.

-- Steve