On Fri, Sep 11, 2026 at 03:21:25PM +0800, Kunwu Chan wrote:
> Atomic SRCU must remain in the small size state. Warn if this
> invariant is violated and avoid transitioning to big in that case.
>
> Signed-off-by: Kunwu Chan <[email protected]>
Very good, queued for further testing and review, thank you!
I folded the new "if" statement onto one line because some years back the
Linux kernel liberated itself from the 80-column constraint imposed by IBM
back in 1928. We can now have up to 100 characters in a line of code. ;-)
Thanx, Paul
> ---
> Changes since v2:
> - Also prevent the transition when the atomic SRCU size-state
> invariant is violated, per Paul McKenney's suggestion.
> -v2:
> https://lore.kernel.org/rcu/[email protected]/
>
> Changes since v1:
> - Drop the !is_atomic guard from v1 and add WARN_ON_ONCE() instead,
> per Paul McKenney's suggestion.
> - v1:
> https://lore.kernel.org/rcu/[email protected]/
> ---
> kernel/rcu/srcutree.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 84c022ec8e09..07db4e459b30 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -1073,8 +1073,11 @@ static void srcu_gp_end(struct srcu_struct *ssp, bool
> is_atomic)
> raw_spin_unlock_irq_rcu_node(sup);
> }
>
> - /* Transition to big if needed. */
> - if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
> + /* Transition to big if needed, but never for atomic SRCU. */
> + if (ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC &&
> + ss_state != SRCU_SIZE_SMALL) {
> + WARN_ON_ONCE(1);
> + } else if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
> if (ss_state == SRCU_SIZE_ALLOC)
> init_srcu_struct_nodes(ssp, GFP_KERNEL);
> else
> --
> 2.43.0
>
>
