linux-kernel - Re: [PATCH] tracing/timerlat: Move hrtimer_init to timerlat

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Date: Thu, 1 Feb 2024 10:05:59 -0800
From: Greg KH <gregkh@...uxfoundation.org>
To: Daniel Bristot de Oliveira <bristot@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] tracing/timerlat: Move hrtimer_init to timerlat_fd open()

On Thu, Feb 01, 2024 at 05:02:56PM +0100, Daniel Bristot de Oliveira wrote:
> On 2/1/24 16:44, Greg KH wrote:
> > On Thu, Feb 01, 2024 at 04:13:39PM +0100, Daniel Bristot de Oliveira wrote:
> >> Currently, the timerlat's hrtimer is initialized at the first read of
> >> timerlat_fd, and destroyed at close(). It works, but it causes an error
> >> if the user program open() and close() the file without reading.
> > 
> > What error exactly happens?  Userspace, or the kernel crashes?
> 
> sorry, kernel crash:
> 
> # echo NO_OSNOISE_WORKLOAD > /sys/kernel/debug/tracing/osnoise/options
> # echo timerlat > /sys/kernel/debug/tracing/current_tracer
> 
> # cat ./timerlat_load.py
> #!/usr/bin/env python3
> 
> timerlat_fd = open("/sys/kernel/tracing/osnoise/per_cpu/cpu0/timerlat_fd", 'r')
> timerlat_fd.close();
> 
> # ./taskset -c 0 ./timerlat_load.py
> <BOOM>

Then obviously, this is a real, functional, change, so say so in the
kernel changelog :)

thanks,

greg k-h