On Mon, Sep 07, 2026 at 03:58:23PM +0800, Kunwu Chan wrote:
> From: Kunwu Chan <[email protected]>
>
> The transition-to-big code path in srcu_gp_end() calls
> init_srcu_struct_nodes() with GFP_KERNEL, which is illegal in the
> atomic context reachable from synchronize_srcu_atomic(). Atomic SRCU
> has no use for the srcu_node combining tree: it has neither callbacks
> nor srcu_barrier() operations, and its grace periods are serialized
> by ->srcu_atomic_gp_flag instead.
>
> Skip this transition entirely for atomic SRCU, which is also defense
> in depth against any path that might wrongly set ->srcu_size_state for
> an atomic srcu_struct.
>
> Signed-off-by: Kunwu Chan <[email protected]>
Again, given that we have this commit, is this patch needed?
4e01d5320a2f ("srcutree: Suppress to-big transition for atomic SRCU")
And again, if so, please tell me what I am missing.
Thanx, Paul
> ---
> kernel/rcu/srcutree.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 01f224a56b41..74acd5645d4c 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -1074,8 +1074,9 @@ 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 (!is_atomic && 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
>
