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Date:	Fri, 12 Feb 2010 15:22:16 -0800 (PST)
From:	Joe Cao <>
Subject: bug and question in tcp stack


I think it is an obvious bug both in the old and latest kernel:

In function net/ipv4/tcp_output.c, tcp_retransmit_skb() returns a NEGTIVE value on failures.  But in net/ipv4/tcp_timer.c, in function tcp_retransmit_timer(), the line

if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {

checks the return value as a positive number, which will never be true.  On failures from tcp_retransmit_skb(), the code will follow the wrong path.

My second question is regarding the function tcp_retransmit_skb().  The first check in the function is copied here:

 	/* Do not sent more than we queued. 1/4 is reserved for possible
	 * copying overhead: fragmentation, tunneling, mangling etc.
	if (atomic_read(&sk->sk_wmem_alloc) >
	    min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
		return -EAGAIN;

My question is if that turns out to be true, which I saw happend, how could the stack get out of the state?  Because all TCP retransmission may fail, no buffer will be released.  The connection is virtually dead.  Is that true?


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