Messages in this thread | | | Date | Mon, 9 May 2011 10:37:54 +0200 | From | Tejun Heo <> | Subject | Re: [PATCH ptrace] ptrace: use GROUP_STOP_TRAPPING for PTRACE_DETACH too |
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Hey, Oleg.
On Sun, May 08, 2011 at 06:07:20PM +0200, Oleg Nesterov wrote: > > for (i = 0; i < 100000; i++) { > > ptrace(PTRACE_ATTACH, tracee, NULL, NULL); > > waitid(P_PID, tracee, &si, WSTOPPED | WNOHANG); > > if (!si.si_pid) > > nr_wait_fails++; > > OK, this is clear, waitid(WSTOPPED | WNOHANG) can fail if it sees the > tracee inside the transition. > > But, > > > if (ptrace(PTRACE_DETACH, tracee, NULL, NULL)) { > > nr_ptrace_fails++; > > I assume this can only fail for the same reason if waitid() fails? > Or there is something else?
Oh yeah, I was just curious about the timing and see how many fail waitid() but succeed ptrace().
> > /* > > * Reinstate GROUP_STOP_PENDING if group stop is in effect and > > - * @child isn't dead. > > + * @child isn't dead. This will trigger TRACED -> RUNNING -> > > + * STOPPED transition. As this transition can affect the next > > + * ptracer if it attaches before the transition completes, set > > + * TRAPPING too. Read comment in ptrace_attach() for more details. > > */ > > if (!(child->flags & PF_EXITING) && > > (child->signal->flags & SIGNAL_STOP_STOPPED || > > child->signal->group_stop_count)) > > - child->group_stop |= GROUP_STOP_PENDING; > > + child->group_stop |= GROUP_STOP_PENDING | GROUP_STOP_TRAPPING; > > This doesn't look safe, see below. We do not know what the tracee does, > it can be even running.
Ah, right. Setting TRAPPING should probably depend on JOBCTL_TRAPPED flag which is added later.
> > static int ptrace_attach(struct task_struct *task) > > { > > - bool wait_trap = false; > > int retval; > > > > audit_ptrace(task); > > @@ -245,7 +247,6 @@ static int ptrace_attach(struct task_str > > if (task_is_stopped(task)) { > > task->group_stop |= GROUP_STOP_PENDING | GROUP_STOP_TRAPPING; > > signal_wake_up(task, 1); > > - wait_trap = true; > > } > > > > spin_unlock(&task->sighand->siglock); > > @@ -256,9 +257,8 @@ unlock_tasklist: > > unlock_creds: > > mutex_unlock(&task->signal->cred_guard_mutex); > > out: > > - if (wait_trap) > > - wait_event(current->signal->wait_chldexit, > > - !(task->group_stop & GROUP_STOP_TRAPPING)); > > + wait_event(current->signal->wait_chldexit, > > + !(task->group_stop & GROUP_STOP_TRAPPING)); > > Suppose that SIGCONT or, worse, SIGKILL comes in between.
Please ignore this one for now. I'll re-do it after the SEIZE series.
Thanks.
-- tejun
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