linux-kernel - Re: Freeing alternatives sections after module init?

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Message-ID: <87d1n1caun.fsf@rustcorp.com.au>
Date:	Wed, 29 Jun 2016 06:03:20 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jessica Yu <jeyu@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Freeing alternatives sections after module init?

Jessica Yu <jeyu@...hat.com> writes:
> Hi Rusty,

Hi Jessica,

> I noticed that the module loader keeps .altinstructions and
> .altinstr_replacement (which are normally freed after kernel init) in
> core memory after module init, so these sections are never freed for
> modules.
>
> In fact, the module loader seems to keep a number of sections normally
> marked between __init_begin and __init_end (which are then freed in
> free_initmem()) in module core memory, for example on x86, there's
> also .parainstructions and .altinstr_aux.
>
> I was just wondering if this discrepancy was intentional :-)
> Shouldn't these sections be freed after init? Though it probably
> doesn't hurt to keep some of these sections in memory,
> .altinstr_replacement is (for whatever reason) an executable section,
> and is technically not needed anymore after apply_alternatives()
> copies the replacement instructions, so it might be good to free it.

No intention on my part!  Definitely nice to fix; I look forward to your
patch.

And sorry for the delay on review of ro_after_init; I'll look at it
today I promise!

Cheers,
Rusty.