| Message ID | 5e369c9aa5889383aece50a6b5c22256b19ab334.1441839128.git.daniel@iogearbox.net |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Daniel Borkmann <daniel@iogearbox.net> Date: Thu, 10 Sep 2015 01:20:46 +0200 > In case of netlink mmap, there can be situations where received frames > have to be placed into the normal receive queue. The ring buffer indicates > this through NL_MMAP_STATUS_COPY, so the user is asked to pick them up > via recvmsg(2) syscall, and to put the slot back to NL_MMAP_STATUS_UNUSED. > > Commit 0ef707700f1c ("netlink: rx mmap: fix POLLIN condition") changed > polling, so that we walk in the worst case the whole ring through the > new netlink_has_valid_frame(), for example, when the ring would have no > NL_MMAP_STATUS_VALID, but at least one NL_MMAP_STATUS_COPY frame. > > Since we do a datagram_poll() already earlier to pick up a mask that could > possibly contain POLLIN | POLLRDNORM already (due to NL_MMAP_STATUS_COPY), > we can skip checking the rx ring entirely. > > In case the kernel is compiled with !CONFIG_NETLINK_MMAP, then all this is > irrelevant anyway as netlink_poll() is just defined as datagram_poll(). > > Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 50889be..72c1330 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -674,12 +674,19 @@ static unsigned int netlink_poll(struct file *file, struct socket *sock, mask = datagram_poll(file, sock, wait); - spin_lock_bh(&sk->sk_receive_queue.lock); - if (nlk->rx_ring.pg_vec) { - if (netlink_has_valid_frame(&nlk->rx_ring)) - mask |= POLLIN | POLLRDNORM; + /* We could already have received frames in the normal receive + * queue, that will show up as NL_MMAP_STATUS_COPY in the ring, + * so if mask contains pollin/etc already, there's no point + * walking the ring. + */ + if ((mask & (POLLIN | POLLRDNORM)) != (POLLIN | POLLRDNORM)) { + spin_lock_bh(&sk->sk_receive_queue.lock); + if (nlk->rx_ring.pg_vec) { + if (netlink_has_valid_frame(&nlk->rx_ring)) + mask |= POLLIN | POLLRDNORM; + } + spin_unlock_bh(&sk->sk_receive_queue.lock); } - spin_unlock_bh(&sk->sk_receive_queue.lock); spin_lock_bh(&sk->sk_write_queue.lock); if (nlk->tx_ring.pg_vec) {
In case of netlink mmap, there can be situations where received frames have to be placed into the normal receive queue. The ring buffer indicates this through NL_MMAP_STATUS_COPY, so the user is asked to pick them up via recvmsg(2) syscall, and to put the slot back to NL_MMAP_STATUS_UNUSED. Commit 0ef707700f1c ("netlink: rx mmap: fix POLLIN condition") changed polling, so that we walk in the worst case the whole ring through the new netlink_has_valid_frame(), for example, when the ring would have no NL_MMAP_STATUS_VALID, but at least one NL_MMAP_STATUS_COPY frame. Since we do a datagram_poll() already earlier to pick up a mask that could possibly contain POLLIN | POLLRDNORM already (due to NL_MMAP_STATUS_COPY), we can skip checking the rx ring entirely. In case the kernel is compiled with !CONFIG_NETLINK_MMAP, then all this is irrelevant anyway as netlink_poll() is just defined as datagram_poll(). Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> --- net/netlink/af_netlink.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)