linux-kernel - Re: [PATCH v15 03/11] livepatch: Consolidate klp

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Message-ID: <alpine.LSU.2.21.1901091535210.12972@pobox.suse.cz>
Date:   Wed, 9 Jan 2019 15:35:49 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Petr Mladek <pmladek@...e.com>
cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jessica Yu <jeyu@...nel.org>
Subject: Re: [PATCH v15 03/11] livepatch: Consolidate klp_free functions

On Wed, 9 Jan 2019, Petr Mladek wrote:

> The code for freeing livepatch structures is a bit scattered and tricky:
> 
>   + direct calls to klp_free_*_limited() and kobject_put() are
>     used to release partially initialized objects
> 
>   + klp_free_patch() removes the patch from the public list
>     and releases all objects except for patch->kobj
> 
>   + object_put(&patch->kobj) and the related wait_for_completion()
>     are called directly outside klp_mutex; this code is duplicated;
> 
> Now, we are going to remove the registration stage to simplify the API
> and the code. This would require handling more situations in
> klp_enable_patch() error paths.
> 
> More importantly, we are going to add a feature called atomic replace.
> It will need to dynamically create func and object structures. We will
> want to reuse the existing init() and free() functions. This would
> create even more error path scenarios.
> 
> This patch implements more straightforward free functions:
> 
>   + checks kobj_added flag instead of @limit[*]
> 
>   + initializes patch->list early so that the check for empty list
>     always works
> 
>   + The action(s) that has to be done outside klp_mutex are done
>     in separate klp_free_patch_finish() function. It waits only
>     when patch->kobj was really released via the _start() part.
> 
> The patch does not change the existing behavior.
> 
> [*] We need our own flag to track that the kobject was successfully
>     added to the hierarchy.  Note that kobj.state_initialized only
>     indicates that kobject has been initialized, not whether is has
>     been added (and needs to be removed on cleanup).
> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: Miroslav Benes <mbenes@...e.cz>
> Cc: Jessica Yu <jeyu@...nel.org>
> Cc: Jiri Kosina <jikos@...nel.org>
> Cc: Jason Baron <jbaron@...mai.com>

Acked-by: Miroslav Benes <mbenes@...e.cz>

Miroslav