Gdb get stuck when debugging linux kernel

[Parmenides <mobile dot parmenides at gmail dot com>]

Hi

I want to debug linux kernel which running in qemu. The target is
connected with the host through it virual serial port and the kernel
runs in the target contains kgdb stub.  The gdb's version is 7.4 and
the linux kernel's version is 3.1. I started qemu with

   qemu -kernel bzImage -initrd image.cpio.gz -append
"kgdboc=ttyS0,115200 kgdbwait" -serial tcp::1234,server

In another console, the gdb was given commands

   (gdb) target remote local:1234
   (gdb) continue
   ^C
   ... ...  can not continue ... ...

Then I pressed Ctrl+C to suspend the target, but got no reply. The gdb
got stuck and lost control to the target. The target's linux was
running normally. It is said that the problem is caused by different
understanding to RSP protocol between gdb and kgdb, but I have no idea
about how to deal with it. Is there any way to resolve it?