linux-kernel - Re: [RESEND][PATCH v3 03/17] module: Properly propagate MODULE_STATE

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Date:   Wed, 25 Mar 2020 18:35:22 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        mhiramat@...nel.org, bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com
Subject: Re: [RESEND][PATCH v3 03/17] module: Properly propagate
 MODULE_STATE_COMING failure

+++ Peter Zijlstra [24/03/20 14:56 +0100]:
>Now that notifiers got unbroken; use the proper interface to handle
>notifier errors and propagate them.
>
>There were already MODULE_STATE_COMING notifiers that failed; notably:
>
> - jump_label_module_notifier()
> - tracepoint_module_notify()
> - bpf_event_notify()
>
>By propagating this error, we fix those users.
>
>Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>Cc: jeyu@...nel.org
>---
> kernel/module.c |   10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -3751,9 +3751,13 @@ static int prepare_coming_module(struct
> 	if (err)
> 		return err;
>
>-	blocking_notifier_call_chain(&module_notify_list,
>-				     MODULE_STATE_COMING, mod);
>-	return 0;
>+	err = blocking_notifier_call_chain_robust(&module_notify_list,
>+			MODULE_STATE_COMING, MODULE_STATE_GOING, mod);
>+	err = notifier_to_errno(err);
>+	if (err)
>+		klp_module_going(mod);
>+
>+	return err;
> }
>
> static int unknown_module_param_cb(char *param, char *val, const char *modname,
>

This looks fine to me - klp_module_going() is only called after
successful klp_module_coming(), and klp_module_going() is fine with
mod->state still being MODULE_STATE_COMING here. Would be good to have
livepatch folks double check. Which reminds me - Miroslav had pointed
out in the past that if there is an error when calling the COMING
notifiers, the GOING notifiers will be called while the mod->state is
still MODULE_STATE_COMING. I've briefly looked through all the module
notifiers and it looks like nobody is looking at mod->state directly
at least.

Acked-by: Jessica Yu <jeyu@...nel.org>