linux-kernel - Re: [for-next][PATCH 15/16] ftrace: Add freeing algorithm to free ftrace_mod

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Message-ID: <CAEi0qNks_DRMNjZU3NHRZ2E-W+iiXaQccH8G7cDLVX5W8OYGQQ@mail.gmail.com>
Date:   Fri, 6 Oct 2017 23:41:25 -0700
From:   "Joel Fernandes (Google)" <joel.opensrc@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [for-next][PATCH 15/16] ftrace: Add freeing algorithm to free ftrace_mod_maps

Hi Steve,

On Fri, Oct 6, 2017 at 11:07 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
>
> The ftrace_mod_map is a descriptor to save module init function names in
> case they were traced, and the trace output needs to reference the function
> name from the function address. But after the function is unloaded, it
> the maps should be freed, as the rest of the function names are as well.

Just checking for my understanding of this patch - wouldn't this also
mean that if there were any look ups of the init functions that may be
needed at trace output time, then those look ups wont be possible any
more after module is unloaded?

I guess having a reference somehow on the ftrace_mod_map descriptor if
there are any entries in the trace buffer that need it can help
prevent that but it could be too expensive for not much return since
most likely the user wouldn't unload modules before trace collection
in normal usage.

thanks,

- Joel