lkml.org 
[lkml]   [2011]   [May]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH ptrace] ptrace: fix signal->wait_chldexit usage in task_clear_group_stop_trapping()
Hello,

On Sun, May 08, 2011 at 05:34:35PM +0200, Oleg Nesterov wrote:
> But this is subjective too, and I agree that the future patches can
> change the current trivial contract. So:
>
> Reviewed-by: Oleg Nesterov <oleg@redhat.com>
>
> I'll add this fix to my tree.

Great, thanks.

> > > Hmm. This is minor and off-topic, but perhaps it makes sense to move
> > > the code which sets/waits GROUP_STOP_TRAPPING from ptrace_attach() to
> > > the separate function, it can be called outside of tasklist_lock and
> > > cred_guard_mutex.
> >
> > I'm confused. It should be set while siglock is held. Which place
> > are you suggesting?
>
> Of course, we should take siglock. I meant, we could probably make
>
> static void ptrace_s_stopped_traced(struct task_struct *task)
> {
> bool wait_trap = false;
>
> spin_lock(&task->sighand->siglock);
> /*
> * If the task is already STOPPED, set GROUP_STOP_PENDING and
> * TRAPPING, and kick it so that it transits to TRACED. TRAPPING
> * will be cleared if the child completes the transition or any
> * event which clears the group stop states happens. We'll wait
> * for the transition to complete before returning from this
> * function.
> *
> * This hides STOPPED -> RUNNING -> TRACED transition from the
> * attaching thread but a different thread in the same group can
> * still observe the transient RUNNING state. IOW, if another
> * thread's WNOHANG wait(2) on the stopped tracee races against
> * ATTACH, the wait(2) may fail due to the transient RUNNING.
> *
> * The following task_is_stopped() test is safe as both transitions
> * in and out of STOPPED are protected by siglock.
> */
> 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);
>
> if (wait_trap)
> wait_event(current->signal->wait_chldexit,
> !(task->group_stop & GROUP_STOP_TRAPPING));
> return retval;
> }
>
> called by ptrace_attach() at the end.

Ah, okay. Yeah, that might be a good idea but in the just posted
patch series, I implemented a different helper and moved the wait back
into ptrace_check_attach(), so if it needs further cleanup, it would
be great if we could do it on top of the series.

Thanks.

--
tejun


\
 
 \ /
  Last update: 2011-05-08 17:59    [from the cache]
©2003-2011 Jasper Spaans