linux-kernel - Re: [PATCH] tracing: Always update snapshot buffer size

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Message-ID: <20231205123514.03244a4e@gandalf.local.home>
Date:   Tue, 5 Dec 2023 12:35:14 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] tracing: Always update snapshot buffer size

On Tue, 5 Dec 2023 11:52:23 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> It use to be that only the top level instance had a snapshot buffer (for
> latency tracers like wakeup and irqsoff). The update of the ring buffer
> size would check if the instance was the top level and if so, it would
> also update the snapshot buffer as it needs to be the same as the main
> buffer.
> 
> Now that lower level instances also has a snapshot buffer, they too need
> to update their snapshot buffer sizes when the main buffer is changed,
> otherwise the following can be triggered:
> 
>  # cd /sys/kernel/tracing
>  # echo 1500 > buffer_size_kb
>  # mkdir instances/foo
>  # echo irqsoff > instances/foo/current_tracer
>  # echo 1000 > instances/foo/buffer_size_kb
> 

Bah, this is only a partial patch, in fact it doesn't even fix the issue.
It fixes another issue that this issue is dependent on.

I'll send out a v2 shortly.

-- Steve