On Mon, Jun 30, 2025 at 07:24:33PM +0200, Jason A. Donenfeld wrote:

On Thu, Jun 19, 2025 at 10:54:59AM -0400, Yury Norov wrote:

quoted

From: Yury Norov [NVIDIA] <yury.norov@gmail.com>

wg_cpumask_choose_online() opencodes cpumask_nth(). Use it and make the
function significantly simpler. While there, fix opencoded cpu_online()
too.

Signed-off-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
---
v1: https://lore.kernel.org/all/20250604233656.41896-1-yury.norov@gmail.com/ (local)
v2:
 - fix 'cpu' undeclared;
 - change subject (Jason);
 - keep the original function structure (Jason);

 drivers/net/wireguard/queueing.h | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/net/wireguard/queueing.h b/drivers/net/wireguard/queueing.h
index 7eb76724b3ed..56314f98b6ba 100644
--- a/drivers/net/wireguard/queueing.h
+++ b/drivers/net/wireguard/queueing.h

@@ -104,16 +104,11 @@ static inline void wg_reset_packet(struct sk_buff *skb, bool encapsulating)
 
 static inline int wg_cpumask_choose_online(int *stored_cpu, unsigned int id)
 {
-	unsigned int cpu = *stored_cpu, cpu_index, i;
+	unsigned int cpu = *stored_cpu;
+
+	if (unlikely(cpu >= nr_cpu_ids || !cpu_online(cpu)))
+		cpu = *stored_cpu = cpumask_nth(id % num_online_cpus(), cpu_online_mask);

I was about to apply this but then it occurred to me: what happens if
cpu_online_mask changes (shrinks) after num_online_cpus() is evaluated?
cpumask_nth() will then return nr_cpu_ids?

It will return >= nd_cpu_ids. The original version based a for-loop
does the same, so I decided that the caller is safe against it.

If not, I can send a v3. But, what should we do - retry, or return a
local cpu? Or something else?

Thanks,
Yury