blob: 2428612454e700ce97597a73a131831dded2b119 [file] [log] [blame]
From d5818b4d2a150f5e1715c568651dda195322d27d Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Wed, 12 Jun 2019 09:52:32 -0700
Subject: [PATCH] net/packet: remove locking from packet_rcv_has_room()
commit 3a2bb84e4aeab5c90d16e1cd17dbaa17631af529 upstream.
__packet_rcv_has_room() can now be run without lock being held.
po->pressure is only a non persistent hint, we can mark
all read/write accesses with READ_ONCE()/WRITE_ONCE()
to document the fact that the field could be written
without any synchronization.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index beb6770c1bec..d0ab6bbbb75c 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1262,15 +1262,13 @@ static int __packet_rcv_has_room(const struct packet_sock *po,
static int packet_rcv_has_room(struct packet_sock *po, struct sk_buff *skb)
{
- int ret;
- bool has_room;
+ int pressure, ret;
- spin_lock_bh(&po->sk.sk_receive_queue.lock);
ret = __packet_rcv_has_room(po, skb);
- has_room = ret == ROOM_NORMAL;
- if (po->pressure == has_room)
- po->pressure = !has_room;
- spin_unlock_bh(&po->sk.sk_receive_queue.lock);
+ pressure = ret != ROOM_NORMAL;
+
+ if (READ_ONCE(po->pressure) != pressure)
+ WRITE_ONCE(po->pressure, pressure);
return ret;
}
@@ -1361,7 +1359,7 @@ static unsigned int fanout_demux_rollover(struct packet_fanout *f,
i = j = min_t(int, po->rollover->sock, num - 1);
do {
po_next = pkt_sk(f->arr[i]);
- if (po_next != po_skip && !po_next->pressure &&
+ if (po_next != po_skip && !READ_ONCE(po_next->pressure) &&
packet_rcv_has_room(po_next, skb) == ROOM_NORMAL) {
if (i != j)
po->rollover->sock = i;
@@ -3351,7 +3349,7 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
if (skb == NULL)
goto out;
- if (pkt_sk(sk)->pressure)
+ if (READ_ONCE(pkt_sk(sk)->pressure))
packet_rcv_has_room(pkt_sk(sk), NULL);
if (pkt_sk(sk)->has_vnet_hdr) {
@@ -4170,8 +4168,8 @@ static __poll_t packet_poll(struct file *file, struct socket *sock,
TP_STATUS_KERNEL))
mask |= EPOLLIN | EPOLLRDNORM;
}
- if (po->pressure && __packet_rcv_has_room(po, NULL) == ROOM_NORMAL)
- po->pressure = 0;
+ if (READ_ONCE(po->pressure) && __packet_rcv_has_room(po, NULL) == ROOM_NORMAL)
+ WRITE_ONCE(po->pressure, 0);
spin_unlock_bh(&sk->sk_receive_queue.lock);
spin_lock_bh(&sk->sk_write_queue.lock);
if (po->tx_ring.pg_vec) {
--
2.27.0