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

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Date:   Sun, 26 Mar 2023 23:22:42 +0800
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Beau Belgrave <beaub@...ux.microsoft.com>,
        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 13:06:59 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> 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.

Yeah, I confirmed that sysctl can be set via kernel parameter. So it is OK
for me to add a sysctl.

Thank you,

> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>