diff options
| author | Eric Dumazet <edumazet@google.com> | 2019-06-12 09:52:32 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2019-06-14 18:52:14 -0700 |
| commit | 3a2bb84e4aeab5c90d16e1cd17dbaa17631af529 (patch) | |
| tree | c49e1fe841e2a01314f4d7454d8472c6fcd7d5df /net/packet | |
| parent | 2c51c6273c73ff04099f48fb42dfdd2acc7a1b70 (diff) | |
| download | lwn-3a2bb84e4aeab5c90d16e1cd17dbaa17631af529.tar.gz lwn-3a2bb84e4aeab5c90d16e1cd17dbaa17631af529.zip | |
net/packet: remove locking from packet_rcv_has_room()
__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>
Diffstat (limited to 'net/packet')
| -rw-r--r-- | net/packet/af_packet.c | 20 |
1 files changed, 9 insertions, 11 deletions
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 860ca3e6abf5..d409e2fdaa7e 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1260,15 +1260,13 @@ 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; } @@ -1353,7 +1351,7 @@ 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; @@ -3310,7 +3308,7 @@ 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) { @@ -4129,8 +4127,8 @@ 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) { |