netdev - [PATCH net 3/5] wireguard: send/receive: cond_resched() when processing worker ringbuffers

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Date:   Wed,  6 May 2020 15:33:04 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     davem@...emloft.net, netdev@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Sultan Alsawaf <sultan@...neltoast.com>,
        Wang Jian <larkwang@...il.com>
Subject: [PATCH net 3/5] wireguard: send/receive: cond_resched() when processing worker ringbuffers

Users with pathological hardware reported CPU stalls on CONFIG_
PREEMPT_VOLUNTARY=y, because the ringbuffers would stay full, meaning
these workers would never terminate. That turned out not to be okay on
systems without forced preemption, which Sultan observed. This commit
adds a cond_resched() to the bottom of each loop iteration, so that
these workers don't hog the core. Note that we don't need this on the
napi poll worker, since that terminates after its budget is expended.

Suggested-by: Sultan Alsawaf <sultan@...neltoast.com>
Reported-by: Wang Jian <larkwang@...il.com>
Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 drivers/net/wireguard/receive.c | 2 ++
 drivers/net/wireguard/send.c    | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/drivers/net/wireguard/receive.c b/drivers/net/wireguard/receive.c
index 267f202f1931..2566e13a292d 100644
--- a/drivers/net/wireguard/receive.c
+++ b/drivers/net/wireguard/receive.c
@@ -516,6 +516,8 @@ void wg_packet_decrypt_worker(struct work_struct *work)
 				&PACKET_CB(skb)->keypair->receiving)) ?
 				PACKET_STATE_CRYPTED : PACKET_STATE_DEAD;
 		wg_queue_enqueue_per_peer_napi(skb, state);
+		if (need_resched())
+			cond_resched();
 	}
 }
 
diff --git a/drivers/net/wireguard/send.c b/drivers/net/wireguard/send.c
index 3e030d614df5..dc3079e17c7f 100644
--- a/drivers/net/wireguard/send.c
+++ b/drivers/net/wireguard/send.c
@@ -281,6 +281,8 @@ void wg_packet_tx_worker(struct work_struct *work)
 
 		wg_noise_keypair_put(keypair, false);
 		wg_peer_put(peer);
+		if (need_resched())
+			cond_resched();
 	}
 }
 
@@ -304,6 +306,8 @@ void wg_packet_encrypt_worker(struct work_struct *work)
 		}
 		wg_queue_enqueue_per_peer(&PACKET_PEER(first)->tx_queue, first,
 					  state);
+		if (need_resched())
+			cond_resched();
 	}
 }
 
-- 
2.26.2