Re: [PATCH v7 05/10] tracing/osnoise: Per-cpu mutexes and fd detachment

[Crystal Wood <crwood@redhat.com>]

On Fri, 2026-11-13 at 07:14 +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential
> issue to consider:
> - [Medium] tracing/osnoise: missing migration detection in
>   timerlat_fd_read()
> --
> 
> commit d34bc9208d90b4be9c903307f53e72248c2ac3b7
> Author: Crystal Wood <crwood@redhat.com>
> 
> tracing/osnoise: Per-cpu mutexes and fd detachment
> 
> This commit introduces per-cpu mutexes to protect kthread and timerlat file
> descriptor state, replacing the SIGKILL mechanism for user-space timerlat
> threads with a mutex-protected detachment mechanism.
> 
> [Severity: Medium]
> In kernel/trace/trace_osnoise.c, timerlat_fd_read() removes the
> cpu != smp_processor_id() migration handling (which set
> cpu_tmr_var(cpu)->uthread_migrate = 1, tainted osnoise, and stopped
> tracing) and instead locks this_cpu_tmr_var()->detach_lock before checking
> fdd != osn_var->fdd or tlat->uthread_migrate.
> 
> Can this miss user-space thread migrations when NO_OSNOISE_WORKLOAD is
> enabled after the timerlat tracer has already been started?
> 
> By default, OSN_WORKLOAD is set in osnoise_options. If the user enables
> timerlat first and then writes NO_OSNOISE_WORKLOAD to osnoise/options (as
> shown in Documentation/trace/timerlat-tracer.rst), osnoise_options_write()
> does not call register_migration_monitor(), which only runs during initial
> tracer startup in osnoise_workload_start() -> osnoise_hook_events() ->
> hook_thread_events() -> register_migration_monitor() and skips registering
> trace_sched_migrate_callback() when OSN_WORKLOAD is set.

That's a minor pre-existing bug that shouldn't block this patchset.

-Crystal