Date: Wed, 10 Jan 2018 22:35:36 -0600
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: jeyu@kernel.org, jikos@kernel.org, linux-kernel@vger.kernel.org,
        live-patching@vger.kernel.org, pmladek@suse.com, jbaron@akamai.com
Subject: Re: [PATCH v2] livepatch: Remove immediate feature
Message-ID: <20180111043536.5hdabug7t2kdk243@treble>
References: <20180110100128.25505-1-mbenes@suse.cz>
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On Wed, Jan 10, 2018 at 11:01:28AM +0100, Miroslav Benes wrote:
> Immediate flag has been used to disable per-task consistency and patch
> all tasks immediately. It could be useful if the patch doesn't change any
> function or data semantics.
> 
> However, it causes problems on its own. The consistency problem is
> currently broken with respect to immediate patches.
> 
> func            a
> patches         1i
>                 2i
>                 3
> 
> When the patch 3 is applied, only 2i function is checked (by stack
> checking facility). There might be a task sleeping in 1i though. Such
> task is migrated to 3, because we do not check 1i in
> klp_check_stack_func() at all.
> 
> Coming atomic replace feature would be easier to implement and more
> reliable without immediate.
> 
> Thus, remove immediate feature completely and save us from the problems.
> 
> Note that force feature has the similar problem. However it is
> considered as a last resort. If used, administrator should not apply any
> new live patches and should plan for reboot into an updated kernel.
> 
> The architectures would now need to provide HAVE_RELIABLE_STACKTRACE to
> fully support livepatch.
> 
> Signed-off-by: Miroslav Benes <mbenes@suse.cz>
> ---
> v2 changes:
> - 2/2 from v1 dropped
> - documentation
> 
>  Documentation/livepatch/livepatch.txt        | 89 +++++++++-------------------
>  include/linux/livepatch.h                    |  4 --
>  kernel/livepatch/core.c                      | 12 +---
>  kernel/livepatch/transition.c                | 49 ++-------------
>  samples/livepatch/livepatch-callbacks-demo.c | 15 -----
>  samples/livepatch/livepatch-sample.c         | 15 -----
>  samples/livepatch/livepatch-shadow-fix1.c    | 15 -----
>  samples/livepatch/livepatch-shadow-fix2.c    | 15 -----
>  8 files changed, 33 insertions(+), 181 deletions(-)

Nice diffstat.

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

-- 
Josh