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

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Date:   Thu, 26 Mar 2020 23:51:19 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, 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, live-patching@...r.kernel.org
Subject: Re: [RESEND][PATCH v3 03/17] module: Properly propagate
 MODULE_STATE_COMING failure

On Wed, Mar 25, 2020 at 06:35:22PM +0100, Jessica Yu wrote:
> +++ 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>

Looks good to me.  klp_module_going() is already called in other
load_module() error scenarios so this should be fine from a livepatch
standpoint.

Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh