Bug in rev 1.3 of sys/i386/linux/linux_ptrace.c

[Marcel Moolenaar]

On Mon, Apr 14, 2003 at 04:12:06PM -0400, John Baldwin wrote:
> In the linux_ptrace() function there is the following code:
*snip*
>                 /* not currently stopped */
>                 if ((p->p_flag & (P_TRACED|P_WAITED)) == 0) {
>                         error = EBUSY;
>                         goto fail;
>                 }
> 
>                 ...
> 
> Now, since we've already checked P_TRACED above, this last
> check will never fail.  The diff in rev 1.3 was:
> 
> -               if (p->p_stat != SSTOP || (p->p_flag & P_WAITED) == 0) {
> +               if ((p->p_flag & (P_TRACED|P_WAITED)) == 0) {
> 
> So should this be (P_STOPPED|P_WAITED) instead?  Or maybe just
> (P_STOPPED_TRACE|P_WAITED)?

I don't know the difference between P_STOPPED and P_STOPPED_TRACE
but yes, we should check whether the process is stopped. The
equivalent in sys/kern/sys_process.c is:

	if (!P_SHOULDSTOP(p) || (p->p_flag & P_WAITED) == 0) {

P_SHOULDSTOP(p) expands to:

	((p)->p_flag & P_STOPPED)

Using P_STOPPED makes us bug-for-bug compatible...

-- 
 Marcel Moolenaar	  USPA: A-39004		 marcel at xcllnt.net