linux-kernel - Re: [PATCH] tracing: fgraph: Protect return handler from recursion loop

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Message-ID: <20250922104228.4993227e@batman.local.home>
Date: Mon, 22 Sep 2025 10:42:28 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Peter Zijlstra
 <peterz@...radead.org>, Steven Rostedt <rostedt@...nel.org>, Menglong Dong
 <menglong8.dong@...il.com>, tglx@...utronix.de, mingo@...hat.com,
 bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 kees@...nel.org, samitolvanen@...gle.com, rppt@...nel.org, luto@...nel.org,
 ast@...nel.org, andrii@...nel.org, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: [PATCH] tracing: fgraph: Protect return handler from recursion
 loop

On Mon, 22 Sep 2025 15:38:13 +0200
Jiri Olsa <olsajiri@...il.com> wrote:

> > I found ftrace_test_recursion_trylock() allows one nest level, can you
> > make sure it is OK?  
> 
> hum, I recall being surprised by that already in the past,
> I thought we fixed that somehow, will check later today

It still does allow one level of recursion, because there's still
locations that can trace in interrupt context before the preempt count
is updated to the new context.

I looked at fixing these, but IIRC, there's several locations in
assembly that do this and it started getting messy. I guess I can try
to fix this again.

-- Steve