From 38ab52e8e1e2dd65f2d349f82553335813b638d2 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 2 Feb 2017 20:40:08 -0800 Subject: [PATCH] tcp: clear pfmemalloc on outgoing skb Josef Bacik diagnosed following problem : I was seeing random disconnects while testing NBD over loopback. This turned out to be because NBD sets pfmemalloc on it's socket, however the receiving side is a user space application so does not have pfmemalloc set on its socket. This means that sk_filter_trim_cap will simply drop this packet, under the assumption that the other side will simply retransmit. Well we do retransmit, and then the packet is just dropped again for the same reason. It seems the better way to address this problem is to clear pfmemalloc in the TCP transmit path. pfmemalloc strict control really makes sense on the receive path. Signed-off-by: Eric Dumazet Acked-by: Josef Bacik Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 956bea9..ccf1ef4 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -964,6 +964,13 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, */ skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1); + /* If we had to use memory reserve to allocate this skb, + * this might cause drops if packet is looped back : + * Other socket might not have SOCK_MEMALLOC. + * Packets not looped back do not care about pfmemalloc. + */ + skb->pfmemalloc = 0; + skb_push(skb, tcp_header_size); skb_reset_transport_header(skb); -- 2.7.4