Subject: [PATCH 44/44] wireguard: send/receive: cond_resched() when processing worker ringbuffers

From: "Jason A. Donenfeld" <[email-masked]>
Date: Wed, 6 May 2020 15:33:04 -0600

[ Upstream commit 4005f5c3c9d006157ba716594e0d70c88a235c5e ]

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 <[email-masked]>
Reported-by: Wang Jian <[email-masked]>
Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
Signed-off-by: Jason A. Donenfeld <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 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 7348c10cbae3..e8a7d0a0cb88 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();
 	}
 }
 
@@ -305,6 +307,8 @@ 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