Re: [PATCH] tracing/osnoise: Fix possible recursive locking for cpus_read_lock()

From: Steven Rostedt
Date: Tue Feb 25 2025 - 11:32:35 EST


On Tue, 25 Feb 2025 12:31:32 +0000
Ran Xiaokai <ranxiaokai627@xxxxxxx> wrote:

> @@ -2097,7 +2096,7 @@ static void osnoise_hotplug_workfn(struct
> work_struct *dummy)
> return;
>
> guard(mutex)(&interface_lock);
> - guard(cpus_read_lock)();
> + cpus_read_lock();
>
> if (!cpu_online(cpu))
> return;

This is buggy. You removed the guard, and right below we have an error exit
that will leave this function without unlocking the cpus_read_lock().

> @@ -2105,7 +2104,12 @@ static void osnoise_hotplug_workfn(struct
> work_struct *dummy)
> if (!cpumask_test_cpu(cpu, &osnoise_cpumask))
> return;
>
> - start_kthread(cpu);
> + if (start_kthread(cpu)) {
> + cpus_read_unlock();
> + stop_per_cpu_kthreads();
> + return;

If all you want to do is to unlock before calling stop_per_cpu_kthreads(),
then this should simply be:

if (start_kthread(cpu)) {
cpus_read_unlock();
stop_per_cpu_kthreads();
cpus_read_lock(); // The guard() above will unlock this
return;
}


But I still have to verify that this is indeed the issue here.

-- Steve


> + }
> + cpus_read_unlock();
> }
>
> static DECLARE_WORK(osnoise_hotplug_work, osnoise_hotplug_workfn);