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Date:   Fri, 27 Mar 2020 13:04:44 +0100 (CET)
From:   Miroslav Benes <mbenes@suse.cz>
To:     Jessica Yu <jeyu@kernel.org>
cc:     Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, rostedt@goodmis.org,
        mhiramat@kernel.org, bristot@redhat.com, jbaron@akamai.com,
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        mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org,
        ard.biesheuvel@linaro.org, jpoimboe@redhat.com
Subject: Re: [RESEND][PATCH v3 03/17] module: Properly propagate MODULE_STATE_COMING
 failure
In-Reply-To: <20200325173519.GA5415@linux-8ccs>
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References: <20200324135603.483964896@infradead.org> <20200324142245.445253190@infradead.org> <20200325173519.GA5415@linux-8ccs>
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On Wed, 25 Mar 2020, 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@infradead.org>
> >Cc: jeyu@kernel.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.

Yes, it is ok.

> 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.

Thanks for double-checking. I triple-checked and yes, it should be fine. 
All module notifiers check the value from the function parameter and not 
mod->state directly.

Reviewed-by: Miroslav Benes <mbenes@suse.cz>

M