Re: [PATCH v4] livepatch/module: Correctly handle coming and going modules

Josh Poimboeuf
2015-03-12T19:23:54Z

On Thu, Mar 12, 2015 at 12:55:13PM +0100, Petr Mladek wrote:
> There is a notifier that handles live patches for coming and going modules.
> It takes klp_mutex lock to avoid races with coming and going patches but
> it does not keep the lock all the time. Therefore the following races are
> possible:
>
> 1. The notifier is called sometime in STATE_MODULE_COMING. The module
> is visible by find_module() in this state all the time. It means that
> new patch can be registered and enabled even before the notifier is
> called. It might create wrong order of stacked patches, see below
> for an example.
>
> 2. New patch could still see the module in the GOING state even after
> the notifier has been called. It will try to initialize the related
> object structures but the module could disappear at any time. There
> will stay mess in the structures. It might even cause an invalid
> memory access.
>
> This patch solves the problem by adding a boolean variable into struct module.
> The value is true after the coming and before the going handler is called.
> New patches need to be applied when the value is true and they need to ignore
> the module when the value is false.

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