kvm tools: Fix use after free during shutdown

kvm tools: Fix use after free during shutdown

Valgrind reports the following use after free error, when shutting down a
guest:

  [penberg@tux kvm]$ valgrind ./vm run

  [ snip ]

  Mounting...
  Starting '/bin/sh'...
  sh-4.2# exit

  [ snip ]

  ==4726== Thread 11:
  ==4726== Invalid read of size 8
  ==4726==    at 0x407818: kvm__continue (kvm.c:518)
  ==4726==    by 0x3DE683534F: ??? (in /lib64/libc-2.14.so)
  ==4726==    by 0x3DE68D8AF6: ioctl (in /lib64/libc-2.14.so)
  ==4726==    by 0x406C95: kvm_cpu__run (kvm-cpu.c:35)
  ==4726==    by 0x406D95: kvm_cpu__start (kvm-cpu.c:109)
  ==4726==    by 0x4046D5: kvm_cpu_thread (builtin-run.c:603)
  ==4726==    by 0x3DE7007B30: start_thread (in /lib64/libpthread-2.14.so)
  ==4726==    by 0x3DE68DFD2C: clone (in /lib64/libc-2.14.so)
  ==4726==  Address 0x4c2e040 is 0 bytes inside a block of size 936 free'd
  ==4726==    at 0x4A055FE: free (vg_replace_malloc.c:366)
  ==4726==    by 0x4046E7: kvm_cpu_thread (builtin-run.c:606)
  ==4726==    by 0x3DE7007B30: start_thread (in /lib64/libpthread-2.14.so)
  ==4726==    by 0x3DE68DFD2C: clone (in /lib64/libc-2.14.so)
  ==4726==
  ==4726== Thread 1:
  ==4726== Invalid read of size 1
  ==4726==    at 0x4057BC: kvm_cmd_run (builtin-run.c:1182)
  ==4726==    by 0x40D46D: handle_command (kvm-cmd.c:84)
  ==4726==    by 0x3DE682139C: (below main) (in /lib64/libc-2.14.so)
  ==4726==  Address 0x4e36f58 is 920 bytes inside a block of size 936 free'd
  ==4726==    at 0x4A055FE: free (vg_replace_malloc.c:366)
  ==4726==    by 0x4046E7: kvm_cpu_thread (builtin-run.c:606)
  ==4726==    by 0x3DE7007B30: start_thread (in /lib64/libpthread-2.14.so)
  ==4726==    by 0x3DE68DFD2C: clone (in /lib64/libc-2.14.so)

This patch fixes the problem by moving the kvm_cpu__delete() call from
kvm_cpu_thread() to kvm_cmd_run() after we've made sure the VCPU thread is
stopped.

Signed-off-by: Pekka Enberg <penberg@kernel.org>