On Thu, 27 Nov 2025 10:22:30 +0100 Ard Biesheuvel <[email protected]> wrote:
> From: Ard Biesheuvel <[email protected]> > > The batched entropy containers each have a generation field, to keep > track of the base_crng generation from which it was last reseeded. > > This use case does not require all bits of the unsigned long to be > stored: storing only 32 bits is sufficient to determine whether or not > we're at most 4 billion generations behind, which seems ample. > > So use an unsigned int instead: this will allow a future patch to treat > the generation and position as a single 64-bit quantity, which can be > used locklessly in a compare-and-exchange() operation. Probably best to use a u32. While it will always(?) be the same as 'unsigned int' it is more descriptive. > > Signed-off-by: Ard Biesheuvel <[email protected]> > --- > drivers/char/random.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index b8b24b6ed3fe..0e04bc60d034 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -507,7 +507,7 @@ struct batch_ ##type { > \ > */ > \ > type entropy[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(type))]; > \ > local_lock_t lock; > \ > - unsigned long generation; > \ > + unsigned int generation; > \ > unsigned int position; > \ > }; > \ > > \ > @@ -521,7 +521,7 @@ type get_random_ ##type(void) > \ > type ret; > \ > unsigned long flags; > \ > struct batch_ ##type *batch; > \ > - unsigned long next_gen; > \ > + unsigned int next_gen; > \ > > \ > warn_unseeded_randomness(); > \ > > \ > @@ -533,7 +533,7 @@ type get_random_ ##type(void) > \ > local_lock_irqsave(&batched_entropy_ ##type.lock, flags); > \ > batch = raw_cpu_ptr(&batched_entropy_##type); > \ > > \ > - next_gen = READ_ONCE(base_crng.generation); > \ > + next_gen = (unsigned int)READ_ONCE(base_crng.generation); > \ Isn't that cast pointless? David > if (batch->position >= ARRAY_SIZE(batch->entropy) || > \ > next_gen != batch->generation) { > \ > _get_random_bytes(batch->entropy, sizeof(batch->entropy)); > \
