linux-kernel - Re: [PATCH] livepatch: Enforce reliable stack trace as config dependency

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Message-ID: <nycvar.YFH.7.76.1904161345560.9803@cbobk.fhfr.pm>
Date:   Tue, 16 Apr 2019 13:47:30 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Petr Mladek <pmladek@...e.com>
cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH] livepatch: Enforce reliable stack trace as config
 dependency

On Tue, 12 Feb 2019, Petr Mladek wrote:

> > I think I'd rather go in the opposite direction: allow the patches to be
> > loaded.  Then they can be forced, if needed.  That enables both compile
> > and runtime testing.  That way we don't make any backward progress,
> > until such arches get reliable stacktraces.
> 
> Do you mean to convert the error into warning?
> 
> For example, the change below. Note that I did not mention
> the possibility to force the transition by intention. It is risky
> and people should not get used to it.
> 
> Heh, I think that this was the main reason why it was the error.
> We did not want to get people used to forcing livepatches.
> 
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index d1af69e9f0e3..8d9bce251516 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -1035,11 +1035,10 @@ int klp_enable_patch(struct klp_patch *patch)
>  		return -ENODEV;
>  
>  	if (!klp_have_reliable_stack()) {
> -		pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
> -		return -EOPNOTSUPP;
> +		pr_warn("This architecture doesn't have support for the livepatch consistency model.\n");
> +		pr_warn("Only one livepatch can be installed.\n");
>  	}
>  
> -

This seems to have been lost.

I think we should take this aproach before Miroslav is ready with 
realiable stack traces for s390. At the same time, I'd suggest issuing a 
proper WARN() there instead of just pr_warn(). The kernel might be in a 
potentially funky state, so let's at least get the 'W' taint in place.

-- 
Jiri Kosina
SUSE Labs