[FreeBSD-6.1 6.2] Race condition could happen while two thread close socket?

[Blue]

Dear all:

When looking into the soclose() in uipc_socket.c, I thought of one 
possible situation.

If thread A called soclose() first, and then execute sorele() then 
sofree(). However, in sofree() (defined in uipc_socket.c), the socket 
mutex and accept mutex is unlocked first before releasing socket send 
buffer. While thread A is dealing with the send buffer releasing, 
another thread, thread B, jumped in. It also calls soclose(), and then 
sorele(). Following will be a catastrophe: sorele() will examine the 
socket's reference count ((so)->so_count), then panic occurs since the 
count value equals zero!

Is there any reasonable explanation?

Thanks.

BR,

Yi-Wen