Hi Thomas,
I'm not a huge fan of this change:
On Thu, Nov 06, 2025 at 11:02:12AM +0100, Thomas Weißschuh wrote:
+static DEFINE_STATIC_KEY_FALSE(random_vdso_is_ready); /* Control how we warn userspace. */ static struct ratelimit_state urandom_warning = @@ -252,6 +253,9 @@ static void random_vdso_update_generation(unsigned long next_gen) if (!IS_ENABLED(CONFIG_VDSO_GETRANDOM)) return;
- if (!static_branch_likely(&random_vdso_is_ready))
return;- /* base_crng.generation's invalid value is ULONG_MAX, while
- vdso_k_rng_data->generation's invalid value is 0, so add one to the
- former to arrive at the latter. Use smp_store_release so that this
@@ -274,6 +278,9 @@ static void random_vdso_set_ready(void) if (!IS_ENABLED(CONFIG_VDSO_GETRANDOM)) return;
- if (!static_branch_likely(&random_vdso_is_ready))
return;- WRITE_ONCE(vdso_k_rng_data->is_ready, true);
} @@ -925,6 +932,9 @@ void __init random_init(void) _mix_pool_bytes(&entropy, sizeof(entropy)); add_latent_entropy();
- if (IS_ENABLED(CONFIG_VDSO_GETRANDOM))
static_branch_enable(&random_vdso_is_ready);- /*
- If we were initialized by the cpu or bootloader before jump labels
- or workqueues are initialized, then we should enable the static
@@ -934,8 +944,10 @@ void __init random_init(void) crng_set_ready(NULL); /* Reseed if already seeded by earlier phases. */
- if (crng_ready())
- if (crng_ready()) { crng_reseed(NULL);
random_vdso_set_ready();- }
The fact that the vdso datapage is set up by the time random_init() is called seems incredibly contingent on init details. Why not, instead, make this a necessary part of the structure of vdso setup code, which can actually know about what happens when? For example, one clean way of doing that would be to make vdso_k_rng_data always valid by having it initially point to __initdata memory, and then when it's time to initialize the real datapage, memcpy() the __initdata memory to the new specially allocated memory. Then we don't need the complex state tracking that this commit and the prior one introduce.
Jason