linux-kernel - Re: [PATCH v8 11/11] tracing/user_events: Limit global user

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Message-ID: <20230324130659.587ecfd2@gandalf.local.home>
Date:   Fri, 24 Mar 2023 13:06:59 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        mathieu.desnoyers@...icios.com, dcook@...ux.microsoft.com,
        alanau@...ux.microsoft.com, brauner@...nel.org,
        akpm@...ux-foundation.org, ebiederm@...ssion.com,
        keescook@...omium.org, tglx@...utronix.de,
        linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v8 11/11] tracing/user_events: Limit global user_event
 count

On Fri, 24 Mar 2023 09:43:53 -0700
Beau Belgrave <beaub@...ux.microsoft.com> wrote:

> > It was actually merged in 5.8. So sysctl should be sufficient with that.
> > But maybe it's weird to start adding sysctls, when the rest of tracing
> > tunables is AFAIK under /sys/kernel/tracing/ ?
> >   
> 
> During the TraceFS meetings Steven runs I was asked to add a boot
> parameter and sysctl for user_events to limit the max.
> 
> To me, it seems when user_events moves toward namespace awareness
> sysctl might be easier to use from within a namespace to turn knobs.
> 
> Happy to change to whatever, but I want to see Steven and Masami agree
> on the approach before doing so.
> 
> Steven, do you agree with Masami to move to just sysctl?

We do have some tracing related sysctls already:

# cd /proc/sys/kernel
# ls *trace*
ftrace_dump_on_oops  oops_all_cpu_backtrace  traceoff_on_warning
ftrace_enabled       stack_tracer_enabled    tracepoint_printk

Although I would love to deprecated ftrace_enable as that now has a
control in tracefs, but it's not unprecedented to have tracing tunables as
sysctl.

And if we get cmdline boot parameters for free from sysctls then all the
better.

-- Steve