[PATCH v4 2/3] prandom: Add __always_inline version of prandom_u32_state()

[Ryan Roberts]

On 28/01/2026 17:00, Jason A. Donenfeld wrote:
> On Mon, Jan 19, 2026 at 01:01:09PM +0000, Ryan Roberts wrote:
>> We will shortly use prandom_u32_state() to implement kstack offset
>> randomization and some arches need to call it from non-instrumentable
>> context. So let's implement prandom_u32_state() as an out-of-line
>> wrapper around a new __always_inline prandom_u32_state_inline(). kstack
>> offset randomization will use this new version.
>>
>> Acked-by: Mark Rutland <mark.rutland at arm.com>
>> Signed-off-by: Ryan Roberts <ryan.roberts at arm.com>
>> ---
>>  include/linux/prandom.h | 20 ++++++++++++++++++++
>>  lib/random32.c          |  8 +-------
>>  2 files changed, 21 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/prandom.h b/include/linux/prandom.h
>> index ff7dcc3fa105..801188680a29 100644
>> --- a/include/linux/prandom.h
>> +++ b/include/linux/prandom.h
>> @@ -17,6 +17,26 @@ struct rnd_state {
>>  	__u32 s1, s2, s3, s4;
>>  };
>>  
>> +/**
>> + * prandom_u32_state_inline - seeded pseudo-random number generator.
>> + * @state: pointer to state structure holding seeded state.
>> + *
>> + * This is used for pseudo-randomness with no outside seeding.
>> + * For more random results, use get_random_u32().
>> + * For use only where the out-of-line version, prandom_u32_state(), cannot be
>> + * used (e.g. noinstr code).
>> + */
>> +static __always_inline u32 prandom_u32_state_inline(struct rnd_state *state)
> 
> This is pretty bikesheddy and I'm not really entirely convinced that my
> intuition is correct here, but I thought I should at least ask. Do you
> think this would be better called __prandom_u32_state(), where the "__"
> is kind of a, "don't use this directly unless you know what you're doing
> because it's sort of internal"? It seems like either we make this inline
> for everybody, or if there's a good reason for having most users use the
> non-inline version, then we should be careful that new users don't use
> the inline version. I was thinking the __ would help with that.

I'm certainly happy to do that, if that's your preference. I have to respin this
anyway, given the noinstr issue.

> 
> Jason