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SubjectRe: [PATCH 1/2] wait/ptrace: always assume __WALL if the child is traced
On Tue, 20 Oct 2015 19:17:54 +0200 Oleg Nesterov <oleg@redhat.com> wrote:

> The following program (simplified version of generated by syzkaller)
>
> #include <pthread.h>
> #include <unistd.h>
> #include <sys/ptrace.h>
> #include <stdio.h>
> #include <signal.h>
>
> void *thread_func(void *arg)
> {
> ptrace(PTRACE_TRACEME, 0,0,0);
> return 0;
> }
>
> int main(void)
> {
> pthread_t thread;
>
> if (fork())
> return 0;
>
> while (getppid() != 1)
> ;
>
> pthread_create(&thread, NULL, thread_func, NULL);
> pthread_join(thread, NULL);
> return 0;
> }
>
> creates the unreapable zombie if /sbin/init doesn't use __WALL.
>
> This is not a kernel bug, at least in a sense that everything works as
> expected: debugger should reap a traced sub-thread before it can reap
> the leader, but without __WALL/__WCLONE do_wait() ignores sub-threads.
>
> Unfortunately, it seems that /sbin/init in most (all?) distributions
> doesn't use it and we have to change the kernel to avoid the problem.

Well, to fix this a distro needs to roll out a new kernel. Or a new
init(8). Is there any reason to believe that distributing/deploying a
new kernel is significantly easier for everyone? Because fixing init
sounds like a much preferable solution to this problem.


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