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SubjectRe: WARNING in do_jobctl_trap
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.

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