tcp: fix possible deadlock in tcp_send_fin() (d83769a5) · Commits · 戴 / test

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 ("tcp: fix tcp fin memory accounting") Fixes: ("tcp: fix tcp fin memory accounting") Signed-off-by:

Eric Dumazet <edumazet@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

+19 −1

Original line number	Diff line number	Diff line
		@@ -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);

Admin message