linux-kernel - Re: [PATCH v2 3/4] module: Properly propagate MODULE_STATE

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Message-ID: <alpine.LSU.2.21.1910081457420.12133@pobox.suse.cz>
Date:   Tue, 8 Oct 2019 15:08:57 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
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, Yonghong Song <yhs@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>, Jessica Yu <jeyu@...nel.org>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH v2 3/4] module: Properly propagate MODULE_STATE_COMING
 failure

On Mon, 7 Oct 2019, Peter Zijlstra wrote:

> 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: Yonghong Song <yhs@...com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Song Liu <songliubraving@...com>
> Cc: Jessica Yu <jeyu@...nel.org>
> Cc: Martin KaFai Lau <kafai@...com>
> ---
>  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;
>  }

It looks almost ok. At least klp_ error handling is correct now. I see
only one possible problem. If there is an error in a MODULE_STATE_COMING 
notifier, all MODULE_STATE_GOING notifiers will be called with mod->state 
set to MODULE_STATE_COMING. Not nice. I don't think it is actually a 
problem, because all notifiers, that I checked, only use the correct value 
(MODULE_STATE_COMING or MODULE_STATE_GOING, coming from the function 
parameter) and not mod->state. Better to doublecheck though.

However, mod->state is not set to MODULE_STATE_GOING anywhere under 
bug_cleanup label in load_module(). That is a bug and it is there 
regardless of this patch.

Jessica?

Regards
Miroslav