From: Oleg Nesterov <oleg@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
strace-devel@lists.sourceforge.net,
Aleksa Sarai <asarai@suse.com>
Subject: Re: strace lockup when tracing exec in go
Date: Fri, 23 Sep 2016 11:50:32 +0200 [thread overview]
Message-ID: <20160923095031.GA14923@redhat.com> (raw)
In-Reply-To: <20160921152946.GA24210@dhcp22.suse.cz>
Sorry for delay, I was offline. I'll try to return to this problem next
week, currently I can't even read this thread but at first glance the
proposed patch(es) do not look right...
On 09/21, Michal Hocko wrote:
>
> The further investigation shown that the tracer (strace) is stuck
> waiting for cred_guard_mutex
> [<0000000000000000>] mm_access+0x22/0xa0
> [<0000000000000000>] process_vm_rw_core.isra.1+0x112/0x6c0
> [<0000000000000000>] process_vm_rw+0xab/0x110
> [<0000000000000000>] SyS_process_vm_readv+0x15/0x20
> [<0000000000000000>] system_call_fastpath+0x16/0x1b
> [<0000000000000000>] 0x7f186f031c3a
> [<0000000000000000>] 0xffffffffffffffff
...
> this however doesn't happen because both threads which are dead
> are zombies waiting to be reaped by the parent and to call their
> release_task->__exit_signal.
Yes, I know, this was already reported. And so far I do not see any
reasonable fix. I _think_ that the "real" fix should rework the
security_bprm_* helpers, but unlikely this is possible.
The trivial test-case:
void *thread(void *arg)
{
ptrace(PTRACE_TRACEME, 0,0,0);
return NULL;
}
int main(void)
{
int pid = fork();
if (!pid) {
pthread_t pt;
pthread_create(&pt, NULL, thread, NULL);
pthread_join(pt, NULL);
execlp("echo", "echo", "passed", NULL);
}
sleep(1);
// or anything else which needs ->cred_guard_mutex,
// say open(/proc/$pid/mem)
ptrace(PTRACE_ATTACH, pid, 0,0);
kill(pid, SIGCONT);
return 0;
}
Oleg.
next prev parent reply other threads:[~2016-09-23 9:51 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-21 15:29 strace lockup when tracing exec in go Michal Hocko
2016-09-22 4:15 ` Mike Galbraith
2016-09-22 8:01 ` Michal Hocko
2016-09-22 8:20 ` Aleksa Sarai
2016-09-22 8:36 ` Michal Hocko
2016-09-22 9:40 ` Mike Galbraith
2016-09-22 9:53 ` Michal Hocko
2016-09-22 10:09 ` Mike Galbraith
2016-09-22 11:09 ` Michal Hocko
2016-09-22 13:53 ` Michal Hocko
2016-09-23 1:17 ` Aleksa Sarai
2016-09-23 10:21 ` Oleg Nesterov
2016-09-23 11:18 ` Michal Hocko
2016-09-23 13:21 ` Oleg Nesterov
2016-09-23 13:40 ` Michal Hocko
2016-09-23 14:07 ` Oleg Nesterov
2016-09-23 14:19 ` Michal Hocko
2016-09-23 9:50 ` Oleg Nesterov [this message]
2016-09-23 11:23 ` Michal Hocko
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