[uml-devel] Re: The current fix-kill patch

[Bodo Stroesser <bstroesser@fujitsu-siemens.com>]

Jeff Dike wrote:
> Here's the latest fix-kill patch in my tree.  Please test and report...
Have tested based on 2.6.9-bb3. I removed "rework-uml-hang-on-2.6.9-host",
added BlaisorBlade's "uml-hang-on-2.6.9-host", and adapted iand added this
new patch. The resulting UML kernel for me works fine on host 2.6.7-skas3-v7
and 2.6.9-skas3-v7.
Next, I tested what happens if the "kill(pid, SIGKILL);" and
"ptrace(PTRACE_CONT, pid);" are removed from os_kill_ptraced_process(), and
it also worked fine.
Since PTRACE_KILL wakes up the ptraced process unconditionally, IMHO
"ptrace(PTRACE_CONT, pid);" has no effect here. And "kill(pid, SIGKILL);"
only is needed, if the ptraced process is not stopped on a ptrace-interception.
Since os_kill_ptraced_process() is called only then, when the ptraced process
is known to be on a ptrace-stop, I would like to remove "kill(pid, SIGKILL);",
too.
os_kill_ptraced_process() is called each time, a process in TT exec()s. Thus
avoiding unneeded calls is a little speedup.

Bodo
> 
> 				Jeff
> 
> # This patch changes how UML kills ptraced processes in order to be more 
> # correct in the presence of the ptrace changes in 2.6.9.  It used to be that
> # ptrace stopped processes could simply be killed and they would go away.  Now,
> # there's a new run state for ptraced processes which doesn't receive signals
> # until they are PTRACE_KILLed or PTRACE_CONTinued.  So, this patch kills the
> # process, as usual, then PTRACE_KILL and PTRACE_CONT.  This is done in
> # os_kill_ptrace_process() for use from skas mode, and in tracer() when it
> # sees a child process getting a SIGKILL.
> Index: 2.6.9/arch/um/kernel/tt/exec_user.c
> ===================================================================
> --- 2.6.9.orig/arch/um/kernel/tt/exec_user.c	2004-11-22 12:18:40.000000000 -0500
> +++ 2.6.9/arch/um/kernel/tt/exec_user.c	2004-11-22 13:24:50.000000000 -0500
> @@ -36,7 +36,7 @@
>  		tracer_panic("do_exec failed to get registers - errno = %d",
>  			     errno);
>  
> -	kill(old_pid, SIGKILL);
> +	os_kill_ptraced_process(old_pid, 0);
>  
>  	if (ptrace(PTRACE_SETOPTIONS, new_pid, 0, (void *)PTRACE_O_TRACESYSGOOD) < 0)
>  		tracer_panic("do_exec: PTRACE_SETOPTIONS failed, errno = %d", errno);
> Index: 2.6.9/arch/um/kernel/tt/process_kern.c
> ===================================================================
> --- 2.6.9.orig/arch/um/kernel/tt/process_kern.c	2004-11-18 21:24:08.000000000 -0500
> +++ 2.6.9/arch/um/kernel/tt/process_kern.c	2004-11-22 12:18:43.000000000 -0500
> @@ -65,7 +65,8 @@
>  		panic("write of switch_pipe failed, err = %d", -err);
>  
>  	reading = 1;
> -	if((from->exit_state == EXIT_ZOMBIE) || (from->exit_state == EXIT_DEAD))
> +	if((from->exit_state == EXIT_ZOMBIE) ||
> +	   (from->exit_state == EXIT_DEAD))
>  		os_kill_process(os_getpid(), 0);
>  
>  	err = os_read_file(from->thread.mode.tt.switch_pipe[0], &c, sizeof(c));
> @@ -82,7 +83,7 @@
>  	prev_sched = current->thread.prev_sched;
>  	if((prev_sched->exit_state == EXIT_ZOMBIE) ||
>  	   (prev_sched->exit_state == EXIT_DEAD))
> -		os_kill_ptraced_process(prev_sched->thread.mode.tt.extern_pid, 1);
> +		os_kill_process(prev_sched->thread.mode.tt.extern_pid, 1);
>  
>  	/* This works around a nasty race with 'jail'.  If we are switching
>  	 * between two threads of a threaded app and the incoming process 
> Index: 2.6.9/arch/um/kernel/tt/tracer.c
> ===================================================================
> --- 2.6.9.orig/arch/um/kernel/tt/tracer.c	2004-11-22 12:18:40.000000000 -0500
> +++ 2.6.9/arch/um/kernel/tt/tracer.c	2004-11-22 13:28:01.000000000 -0500
> @@ -320,7 +320,13 @@
>  				case OP_HALT:
>  					unmap_physmem();
>  					kmalloc_ok = 0;
> -					ptrace(PTRACE_KILL, pid, 0, 0);
> +					os_kill_ptraced_process(pid, 0);
> +					/* Now let's reap remaining zombies */
> +					errno = 0;
> +					do {
> +						waitpid(-1, &status, 
> +							WUNTRACED);
> +					} while (errno != ECHILD);
>  					return(op == OP_REBOOT);
>  				case OP_NONE:
>  					printf("Detaching pid %d\n", pid);
> Index: 2.6.9/arch/um/os-Linux/process.c
> ===================================================================
> --- 2.6.9.orig/arch/um/os-Linux/process.c	2004-11-18 21:24:08.000000000 -0500
> +++ 2.6.9/arch/um/os-Linux/process.c	2004-11-22 12:18:43.000000000 -0500
> @@ -95,9 +95,16 @@
>  		
>  }
>  
> +/* Kill off a ptraced child by all means available.  kill it normally first,
> + * then PTRACE_KILL it, then PTRACE_CONT it in case it's in a run state from
> + * which it can't exit directly.
> + */
> +
>  void os_kill_ptraced_process(int pid, int reap_child)
>  {
> +	kill(pid, SIGKILL);
>  	ptrace(PTRACE_KILL, pid);
> +	ptrace(PTRACE_CONT, pid);
>  	if(reap_child)
>  		CATCH_EINTR(waitpid(pid, NULL, 0));
>  }
> 



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