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Message-ID: <20160127160457.GA14320@redhat.com>
Date: Wed, 27 Jan 2016 17:04:57 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"Amanieu d'Antras" <amanieu@...il.com>,
Richard Weinberger <richard@....at>,
Davidlohr Bueso <dave@...olabs.net>,
Vladimir Davydov <vdavydov@...allels.com>,
Palmer Dabbelt <palmer@...belt.com>,
Andy Lutomirski <luto@...capital.net>,
LKML <linux-kernel@...r.kernel.org>,
syzkaller <syzkaller@...glegroups.com>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
Eric Dumazet <edumazet@...gle.com>
Subject: Re: 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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