linux-kernel - Re: [PATCH 2/3] modules: set mod->state to GOING before going notifiers are called

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Message-ID: <87a8m7ko6j.fsf@rustcorp.com.au>
Date:	Thu, 10 Mar 2016 13:57:16 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jessica Yu <jeyu@...hat.com>, Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Miroslav Benes <mbenes@...e.cz>, Petr Mladek <pmladek@...e.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jessica Yu <jeyu@...hat.com>
Subject: Re: [PATCH 2/3] modules: set mod->state to GOING before going notifiers are called

Jessica Yu <jeyu@...hat.com> writes:
> In load_module(), the going notifiers are called during error handling
> when an error occurs after the coming notifiers have already been called.
> However, a module's state is still MODULE_STATE_COMING when the going
> notifiers are called in the error path. To be consistent, also set
> mod->state to MODULE_STATE_GOING before calling the going notifiers.
>
> Signed-off-by: Jessica Yu <jeyu@...hat.com>
> ---
>  kernel/module.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 1981ae0..9e80576 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3494,6 +3494,9 @@ static int load_module(struct load_info *info, const char __user *uargs,
>  	return do_init_module(mod);
>  
>   coming_cleanup:
> +	mutex_lock(&module_mutex);
> +	mod->state = MODULE_STATE_GOING;
> +	mutex_unlock(&module_mutex);
>  	blocking_notifier_call_chain(&module_notify_list,
>  				     MODULE_STATE_GOING, mod);

Actually, reviewing this patch makes me realize it is wrong.

We rely on the state of the module being MODULE_STATE_COMING here:

        static inline int strong_try_module_get(struct module *mod)
        {
        	BUG_ON(mod && mod->state == MODULE_STATE_UNFORMED);
        	if (mod && mod->state == MODULE_STATE_COMING)
                	return -EBUSY;

We will just have to document that the notifier can be called with
a module in MODULE_STATE_COMING if it never succeeded its
initialization.

Sorry for the previously false lead,
Rusty.