Messages in this thread | | | Date | Fri, 23 Sep 2016 11:50:32 +0200 | From | Oleg Nesterov <> | Subject | Re: strace lockup when tracing exec in go |
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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.
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