Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 24 Apr 2019 10:51:20 -0500
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Petr Mladek <pmladek@suse.com>
Cc:     Jiri Kosina <jikos@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
        live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] livepatch: Convert error about unsupported reliable
 stacktrace into a warning
Message-ID: <20190424155120.pnau7k4qaavplpnv@treble>
References: <20190424085550.29612-1-pmladek@suse.com>
 <20190424085550.29612-2-pmladek@suse.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20190424085550.29612-2-pmladek@suse.com>
User-Agent: NeoMutt/20180716
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Apr 24, 2019 at 10:55:48AM +0200, Petr Mladek wrote:
> The commit d0807da78e11d46f ("livepatch: Remove immediate feature") caused
> that any livepatch was refused when reliable stacktraces were not supported
> on the given architecture.
> 
> The limitation is too strong. User space processes are safely migrated
> even when entering or leaving the kernel. Kthreads transition would
> need to get forced. But it is safe when:
> 
>    + The livepatch does not change the semantic of the code.
>    + Callbacks do not depend on a safely finished transition.
> 
> Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> ---
>  kernel/livepatch/core.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index eb0ee10a1981..14f33ab6c583 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -1003,11 +1003,10 @@ 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("The livepatch transition may never complete.\n");
>  	}
>  
> -
>  	mutex_lock(&klp_mutex);
>  
>  	ret = klp_init_patch_early(patch);
> -- 
> 2.16.4
> 

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

-- 
Josh