Re: [RFC PATCH 3/7] module: [

[Nadav Amit]

> On 18 Apr 2024, at 13:20, Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> 
> On Tue, Apr 16, 2024 at 12:36:08PM +0300, Nadav Amit wrote:
>> 
>> 
>> 
>> I might be missing something, but it seems a bit racy.
>> 
>> IIUC, module_finalize() calls alternatives_smp_module_add(). At this
>> point, since you don’t hold the text_mutex, some might do text_poke(),
>> e.g., by enabling/disabling static-key, and the update would be
>> overwritten. No?
> 
> Right :(
> Even worse, for UP case alternatives_smp_unlock() will "patch" still empty
> area.
> 
> So I'm thinking about calling alternatives_smp_module_add() from an
> additional callback after the execmem_update_copy().
> 
> Does it make sense to you?

Going over the code again - I might have just been wrong: I confused the
alternatives and the jump-label mechanisms (as they do share a lot of
code and characteristics).

The jump-labels are updated when prepare_coming_module() is called, which
happens after post_relocation() [which means they would be updated using
text_poke() “inefficiently” but should be safe].

The “alternatives” appear only to use text_poke() (in contrast for
text_poke_early()) from very specific few flows, e.g., 
common_cpu_up() -> alternatives_enable_smp().

Are those flows pose a problem after boot?

Anyhow, sorry for the noise.