Re: [PATCH v5 1/7] mm: Restore init_on_* static branch defaults

[Andrew Morton]

On Tue,  9 Mar 2021 13:42:55 -0800 Kees Cook <keescook@xxxxxxxxxxxx> wrote:

> Choosing the initial state of static branches changes the assembly layout
> (if the condition is expected to be likely, inline, or unlikely, out of
> line via a jump). The _TRUE/_FALSE defines for CONFIG_INIT_ON_*_DEFAULT_ON
> were accidentally removed. These need to stay so that the CONFIG controls
> the pessimization of the resulting static branch NOP/JMP locations.

Changelog doesn't really explain why anyone would want to apply this
patch.  This is especially important for -stable patches.

IOW, what is the user visible effect of the bug?