From d83769a580f1132ac26439f50068a29b02be535e Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 21 Apr 2015 18:32:24 -0700 Subject: [PATCH] tcp: fix possible deadlock in tcp_send_fin() Using sk_stream_alloc_skb() in tcp_send_fin() is dangerous in case a huge process is killed by OOM, and tcp_mem[2] is hit. To be able to free memory we need to make progress, so this patch allows FIN packets to not care about tcp_mem[2], if skb allocation succeeded. In a follow-up patch, we might abort tcp_send_fin() infinite loop in case TIF_MEMDIE is set on this thread, as memory allocator did its best getting extra memory already. This patch reverts d22e15371811 ("tcp: fix tcp fin memory accounting") Fixes: d22e15371811 ("tcp: fix tcp fin memory accounting") Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 8c8d7e06b72f..2ade67b7cdb0 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2812,6 +2812,21 @@ begin_fwd: } } +/* We allow to exceed memory limits for FIN packets to expedite + * connection tear down and (memory) recovery. + * Otherwise tcp_send_fin() could loop forever. + */ +static void sk_forced_wmem_schedule(struct sock *sk, int size) +{ + int amt, status; + + if (size <= sk->sk_forward_alloc) + return; + amt = sk_mem_pages(size); + sk->sk_forward_alloc += amt * SK_MEM_QUANTUM; + sk_memory_allocated_add(sk, amt, &status); +} + /* Send a fin. The caller locks the socket for us. This cannot be * allowed to fail queueing a FIN frame under any circumstances. */ @@ -2834,11 +2849,14 @@ void tcp_send_fin(struct sock *sk) } else { /* Socket is locked, keep trying until memory is available. */ for (;;) { - skb = sk_stream_alloc_skb(sk, 0, sk->sk_allocation); + skb = alloc_skb_fclone(MAX_TCP_HEADER, + sk->sk_allocation); if (skb) break; yield(); } + skb_reserve(skb, MAX_TCP_HEADER); + sk_forced_wmem_schedule(sk, skb->truesize); /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */ tcp_init_nondata_skb(skb, tp->write_seq, TCPHDR_ACK | TCPHDR_FIN); -- 2.20.1