Re: More waitpid issues with CLONE_DETACHED/CLONE_THREAD
From: Daniel Jacobowitz
Date: Sun Feb 01 2004 - 19:54:16 EST
On Sun, Feb 01, 2004 at 01:41:48PM -0800, Linus Torvalds wrote:
>
>
> On Sun, 1 Feb 2004, Daniel Jacobowitz wrote:
> >
> > Here you go. The bug turns out not to be related directly to
> > CLONE_DETACHED. Compile testcase with -DNOTHREAD to use fork (well,
> > clone, but without the fancy flags), without -DNOTHREAD to use
> > CLONE_DETACHED | CLONE_THREAD.
>
> I don't think this bug has anything to do with anything else.
>
> This program seems to show that PTRACE_KILL simply doesn't work.
> and the thing is, it looks like the signal handling changes have totally
> made the child ignore the "exit_code" thing, unless I'm seriously
> misreading something.
That may be (though I don't think so) but it reproduces without
PTRACE_KILL too. Try the attached, which just replaced PTRACE_KILL
with PTRACE_CONT/tkill(pid, SIGKILL). Still get zombies. I haven't
tried reproducing entirely without ptrace yet.
> Roland, you know this code better than I do. Any comments?
>
> I suspect the PTRACE_KILL logic should also do a
>
> spin_lock_irqsave(child->sighand->siglock, flags);
> sigaddset(&child->pending->signal, SIGKILL);
> set_tsk_thread_flag(child, TIF_SIGPENDING);
> spin_unlock_irqrestore(child->sighand->siglock, flags);
>
> ptrace_detach(child);
>
> which would set the SIGKILL thing properly, but I suspect we had a good
> reason not to do it that way originally.
>
> Daniel?
I doubt there was a good reason. This code hasn't changed in a hell of
a long time - it probably predates everything up there except sigaddset
:).
/* -DBUG to kill the parent before the child -> hang. */
/* -DNOTHREAD to us fork instead of clone. */
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <signal.h>
#include <sys/ptrace.h>
#include <sched.h>
#include <sys/wait.h>
#include <linux/ptrace.h>
int stack_one[8192], stack_two[8192];
int thread_func_two()
{
write (1, "Thread 2\n", 9);
while (1)
sleep (1);
}
int thread_func_one()
{
int ret;
char retstr[10];
write (1, "Thread 1\n", 9);
ptrace (PTRACE_TRACEME, 0, 0, 0);
write (1, "Thread 1 signalling\n", 20);
syscall (SYS_tkill, getpid (), SIGUSR1);
write (1, "Thread 1 cloning\n", 17);
ret = clone (thread_func_two, stack_two + 8192,
#ifdef NOTHREAD
SIGCHLD,
#else
CLONE_DETACHED | CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_FS,
#endif
NULL);
sprintf (retstr, "= %d\n", ret);
write (1, retstr, strlen (retstr));
write (1, "Thread 1 sleeping\n", 18);
while (1)
sleep (1);
}
int main()
{
int ret, wstat;
int child = fork(), child2 = 0;
if (child == 0)
return thread_func_one();
ptrace (PTRACE_SETOPTIONS, child, 0, PTRACE_O_TRACECLONE | PTRACE_O_TRACEFORK);
ret = waitpid (child, &wstat, __WALL);
ptrace (PTRACE_CONT, child, 0, 0);
ret = waitpid (child, &wstat, __WALL);
ptrace (PTRACE_GETEVENTMSG, child, 0, &child2);
ret = waitpid (child2, &wstat, __WALL);
ptrace (PTRACE_CONT, child, 0, 0);
ptrace (PTRACE_CONT, child2, 0, 0);
#ifndef BUG
ptrace (PTRACE_CONT, child2, 0, 0);
syscall (SYS_tkill, child2, SIGKILL);
ret = waitpid (child2, &wstat, __WALL);
#endif
ptrace (PTRACE_CONT, child, 0, 0);
syscall (SYS_tkill, child, SIGKILL);
ret = waitpid (child, &wstat, __WALL);
#ifdef BUG
ptrace (PTRACE_CONT, child2, 0, 0);
syscall (SYS_tkill, child2, SIGKILL);
ret = waitpid (child2, &wstat, __WALL);
#endif
return 0;
}
--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer
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