linux-kernel - Re: [PATCH 6/7] livepatch: Remove module_disable

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Message-ID: <20200415150216.GA6164@linux-8ccs.fritz.box>
Date:   Wed, 15 Apr 2020 17:02:16 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 6/7] livepatch: Remove module_disable_ro() usage

+++ Josh Poimboeuf [14/04/20 11:28 -0500]:
>With arch_klp_init_object_loaded() gone, and apply_relocate_add() now
>using text_poke(), livepatch no longer needs to use module_disable_ro().
>
>The text_mutex usage can also be removed -- its purpose was to protect
>against module permission change races.
>
>Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
>---
> kernel/livepatch/core.c | 8 --------
> 1 file changed, 8 deletions(-)
>
>diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
>index 817676caddee..3a88639b3326 100644
>--- a/kernel/livepatch/core.c
>+++ b/kernel/livepatch/core.c
>@@ -767,10 +767,6 @@ static int klp_init_object_loaded(struct klp_patch *patch,
> 	struct klp_modinfo *info = patch->mod->klp_info;
>
> 	if (klp_is_module(obj)) {
>-
>-		mutex_lock(&text_mutex);
>-		module_disable_ro(patch->mod);
>-

Don't you still need the text_mutex to use text_poke() though?
(Through klp_write_relocations -> apply_relocate_add -> text_poke)
At least, I see this assertion there:

void *text_poke(void *addr, const void *opcode, size_t len)
{
	lockdep_assert_held(&text_mutex);

	return __text_poke(addr, opcode, len);
}

Jessica