linux-kernel - Re: [PATCH] tracing/osnoise: Fix OSN

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Message-ID: <20260115105237.3788e1be@fedora>
Date: Thu, 15 Jan 2026 10:52:37 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Tomas Glozar <tglozar@...hat.com>
Cc: Crystal Wood <crwood@...hat.com>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 John Kacur <jkacur@...hat.com>, Luis Goncalves <lgoncalv@...hat.com>, LKML
 <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/osnoise: Fix OSN_WORKLOAD-related crash

On Thu, 15 Jan 2026 14:32:27 +0100
Tomas Glozar <tglozar@...hat.com> wrote:

> > Of course, this is complicated by stop_per_cpu_kthreads() happening
> > before interface_lock is acquired.  Do we know why that happens outside
> > the lock?  That might even be the actual cause of this bug.  
> 
> Before commit b484a02c9c ("tracing/timerlat: Drop interface_lock in
> stop_kthread()"), stop_kthread() took interface_lock, so
> stop_per_cpu_kthreads() couldn't be called while holding
> interface_lock. As that is no longer the case, the position of taking
> interface_lock in osnoise_options_write() could be re-evaluated
> (comment in 5bfbcd1ee57b says interface_lock cannot be taken at the
> same time as cpu_read_lock).

Right. Also take a look at commit 177e1cc2f4123 ("tracing/osnoise: Use
a cpumask to know what threads are kthreads"). I don't remember the
details but there was a lot of issues with lock ordering between the
interface_lock and the cpu_read_lock. Whatever changes you make, make
sure to run lockdep while doing your tests.

-- Steve