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Subject: Re: [RFC PATCH 3/7] module: [
From: Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <ZiDz4YbIHEOAnpwF@kernel.org>
Date: Thu, 18 Apr 2024 22:31:16 +0300
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To: Mike Rapoport <rppt@kernel.org>


> On 18 Apr 2024, at 13:20, Mike Rapoport <rppt@kernel.org> wrote:
>=20
> On Tue, Apr 16, 2024 at 12:36:08PM +0300, Nadav Amit wrote:
>>=20
>>=20
>>=20
>> I might be missing something, but it seems a bit racy.
>>=20
>> IIUC, module_finalize() calls alternatives_smp_module_add(). At this
>> point, since you don=E2=80=99t hold the text_mutex, some might do =
text_poke(),
>> e.g., by enabling/disabling static-key, and the update would be
>> overwritten. No?
>=20
> Right :(
> Even worse, for UP case alternatives_smp_unlock() will "patch" still =
empty
> area.
>=20
> So I'm thinking about calling alternatives_smp_module_add() from an
> additional callback after the execmem_update_copy().
>=20
> 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() =E2=80=9Cinefficiently=E2=80=9D but should be safe].

The =E2=80=9Calternatives=E2=80=9D appear only to use text_poke() (in =
contrast for
text_poke_early()) from very specific few flows, e.g.,=20
common_cpu_up() -> alternatives_enable_smp().

Are those flows pose a problem after boot?

Anyhow, sorry for the noise.=