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wireguard: queueing: use saner cpu selection wrapping

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Using `% nr_cpumask_bits` is slow and complicated, and not totally
robust toward dynamic changes to CPU topologies. Rather than storing the
next CPU in the round-robin, just store the last one, and also return
that value. This simplifies the loop drastically into a much more common
pattern.

Fixes: e7096c131e ("net: WireGuard secure network tunnel")
Cc: stable@vger.kernel.org
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: Manuel Leiner <manuel.leiner@gmx.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason A. Donenfeld 2023-07-03 03:27:04 +02:00 committed by David S. Miller
parent a27ac53909
commit 7387943fa3
4 changed files with 14 additions and 16 deletions
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1
drivers/net/wireguard/queueing.c
View File

@ -28,6 +28,7 @@ int wg_packet_queue_init(struct crypt_queue *queue, work_func_t function,
int ret;
memset(queue, 0, sizeof(*queue));
queue->last_cpu = -1;
ret = ptr_ring_init(&queue->ring, len, GFP_KERNEL);
if (ret)
return ret;

25
drivers/net/wireguard/queueing.h
View File

@ -117,20 +117,17 @@ static inline int wg_cpumask_choose_online(int *stored_cpu, unsigned int id)
return cpu;
}
/* This function is racy, in the sense that next is unlocked, so it could return
* the same CPU twice. A race-free version of this would be to instead store an
* atomic sequence number, do an increment-and-return, and then iterate through
* every possible CPU until we get to that index -- choose_cpu. However that's
* a bit slower, and it doesn't seem like this potential race actually
* introduces any performance loss, so we live with it.
/* This function is racy, in the sense that it's called while last_cpu is
* unlocked, so it could return the same CPU twice. Adding locking or using
* atomic sequence numbers is slower though, and the consequences of racing are
* harmless, so live with it.
*/
static inline int wg_cpumask_next_online(int *next)
static inline int wg_cpumask_next_online(int *last_cpu)
{
int cpu = *next;
while (unlikely(!cpumask_test_cpu(cpu, cpu_online_mask)))
cpu = cpumask_next(cpu, cpu_online_mask) % nr_cpumask_bits;
*next = cpumask_next(cpu, cpu_online_mask) % nr_cpumask_bits;
int cpu = cpumask_next(*last_cpu, cpu_online_mask);
if (cpu >= nr_cpu_ids)
cpu = cpumask_first(cpu_online_mask);
*last_cpu = cpu;
return cpu;
}
@ -159,7 +156,7 @@ static inline void wg_prev_queue_drop_peeked(struct prev_queue *queue)
static inline int wg_queue_enqueue_per_device_and_peer(
struct crypt_queue *device_queue, struct prev_queue *peer_queue,
struct sk_buff *skb, struct workqueue_struct *wq, int *next_cpu)
struct sk_buff *skb, struct workqueue_struct *wq)
{
int cpu;
@ -173,7 +170,7 @@ static inline int wg_queue_enqueue_per_device_and_peer(
/* Then we queue it up in the device queue, which consumes the
* packet as soon as it can.
*/
cpu = wg_cpumask_next_online(next_cpu);
cpu = wg_cpumask_next_online(&device_queue->last_cpu);
if (unlikely(ptr_ring_produce_bh(&device_queue->ring, skb)))
return -EPIPE;
queue_work_on(cpu, wq, &per_cpu_ptr(device_queue->worker, cpu)->work);

2
drivers/net/wireguard/receive.c
View File

@ -524,7 +524,7 @@ static void wg_packet_consume_data(struct wg_device *wg, struct sk_buff *skb)
goto err;
ret = wg_queue_enqueue_per_device_and_peer(&wg->decrypt_queue, &peer->rx_queue, skb,
wg->packet_crypt_wq, &wg->decrypt_queue.last_cpu);
wg->packet_crypt_wq);
if (unlikely(ret == -EPIPE))
wg_queue_enqueue_per_peer_rx(skb, PACKET_STATE_DEAD);
if (likely(!ret || ret == -EPIPE)) {

2
drivers/net/wireguard/send.c
View File

@ -318,7 +318,7 @@ static void wg_packet_create_data(struct wg_peer *peer, struct sk_buff *first)
goto err;
ret = wg_queue_enqueue_per_device_and_peer(&wg->encrypt_queue, &peer->tx_queue, first,
wg->packet_crypt_wq, &wg->encrypt_queue.last_cpu);
wg->packet_crypt_wq);
if (unlikely(ret == -EPIPE))
wg_queue_enqueue_per_peer_tx(first, PACKET_STATE_DEAD);
err: