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Date: Mon, 19 May 2025 11:33:39 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
 bpf@vger.kernel.org, x86@kernel.org, Masami Hiramatsu
 <mhiramat@kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Josh Poimboeuf <jpoimboe@kernel.org>, Peter Zijlstra
 <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Jiri Olsa
 <jolsa@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Borislav Petkov
 <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, "H. Peter Anvin"
 <hpa@zytor.com>, Andrii Nakryiko <andrii@kernel.org>
Subject: Re: [PATCH v9 00/13] unwind_user: x86: Deferred unwinding
 infrastructure
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On Fri, 16 May 2025 16:39:56 -0700
Namhyung Kim <namhyung@kernel.org> wrote:

> Hi Steve,
> 
> On Wed, May 14, 2025 at 01:27:20PM -0400, Steven Rostedt wrote:
> > On Tue, 13 May 2025 18:34:35 -0400
> > Steven Rostedt <rostedt@goodmis.org> wrote:
> >   
> > > This has modifications in x86 and I would like it to go through the x86
> > > tree. Preferably it can go into this merge window so we can focus on getting
> > > perf and ftrace to work on top of this.  
> > 
> > I think it may be best for me to remove the two x86 specific patches, and
> > rebuild the ftrace work on top of it. For testing, I'll just keep those two
> > patches in my tree locally, but then I can get this moving for this merge
> > window.  
> 
> Maybe I asked this before but I don't remember if I got the answer. :)
> How does it handle task exits as it won't go to userspace?  I guess it'll
> lose user callstacks for exit syscalls and other termination paths.
> 
> Similarly, it will miss user callstacks in the samples at the end of
> profiling if the target tasks remain in the kernel (or they sleep).
> It looks like a fundamental limitation of the deferred callchains.
> 

Ah, I think I forgot about that. I believe the exit path can also be a
faultable path. All it needs is a hook to do the exit. Is there any
"task work" clean up on exit? I need to take a look.

-- Steve