Re: WARNING in do_jobctl_trap

[Oleg Nesterov]

On 01/26, Oleg Nesterov wrote:
>
> On 01/26, Dmitry Vyukov wrote:
> >
> > Hello,
> >
> > The following program triggers WARN_ON_ONCE(!signr) in do_jobctl_trap:
>
> Can't reproduce, but most probably I understand the problem... I'll try to
> make the simplified test-case tomorrow, it should work if I am right.

This triggers the same problem immediately:


        #include <unistd.h>
        #include <sys/ptrace.h>
        #include <sys/wait.h>

        void test(void)
        {
                for (;;) {
                        if (fork()) {
                                wait(NULL);
                                continue;
                        }

                        ptrace(PTRACE_SEIZE, getppid(), 0, 0);
                        ptrace(PTRACE_INTERRUPT, getppid(), 0, 0);
                        _exit(0);
                }
        }

        int main(void)
        {
                int np;

                for (np = 0; np < 8; ++np)
                        if (!fork())
                                test();

                while (wait(NULL) > 0)
                        ;
                return 0;
        }

and just in case, your test-case works too if I run

        perl -e 'fork; fork; fork; 1 while 1' &

in the background, it has too many delays to work on the idle system.

> Does it work for you reliably?  If yes, any chance you can try the patch
> below?
>
> Oleg.
>
> --- x/kernel/ptrace.c
> +++ x/kernel/ptrace.c
> @@ -73,11 +73,11 @@ void __ptrace_unlink(struct task_struct *child)
>  {
>       BUG_ON(!child->ptrace);
>
> -     child->ptrace = 0;
>       child->parent = child->real_parent;
>       list_del_init(&child->ptrace_entry);
>
>       spin_lock(&child->sighand->siglock);
> +     child->ptrace = 0;
>
>       /*
>        * Clear all pending traps and TRAPPING.  TRAPPING should be

The change above helps, but I need to think more...

Oleg.