Re: [PATCH] tracing/osnoise: Fix OSN_WORKLOAD-related crash

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 15 Jan 2026 14:32:27 +0100
Tomas Glozar <tglozar@redhat.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