| Re: [PATCH][usercr]: Ghost tasks must be detached [message #41623 is a reply to message #41622] |
Thu, 10 February 2011 18:04   |
Louis Rilling
Messages: 7
Registered: February 2011
|
Junior Member |
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On 10/02/11 9:54 -0800, Sukadev Bhattiprolu wrote:
> Louis Rilling [Louis.Rilling@kerlabs.com] wrote:
> | > I can reproduce a crash with 2.6.32 - where if container-init terminates
> | > before a detached child, we get a crash when the detached child calls
> | > proc_flush_mnt(). I suspected it was because do_wait_thread() skipped
> | > over detached tasks (in 2.6.32).
> | >
> | > The same test case does not crash on 2.6.37 - which includes the above commit.
> | > The removes the check for detached tasks, my initial guess is that the above
> | > commit, may have contributed to _fixing_ the crash in 2.6.37.
> |
> | Hm, I don't see how this commit changed things for detached tasks, unless ptrace
> | is involved. Detached tasks go atomically
> | from ->exit_state == 0 to ->exit_state == EXIT_DEAD in exit_notify(),
> | because tracehook_notify_death() returns DEATH_REAP for all not ptraced detached
> | tasks.
> |
> | What do you think has changed precisely?
>
> Well, one of the changes in the commit is this:
>
> @@ -1551,14 +1554,9 @@ static int do_wait_thread(struct wait_opts *wo, struct task_struct *tsk)
> struct task_struct *p;
>
> list_for_each_entry(p, &tsk->children, sibling) {
> - /*
> - * Do not consider detached threads.
> - */
> - if (!task_detached(p)) {
> - int ret = wait_consider_task(wo, 0, p);
> - if (ret)
> - return ret;
> - }
> + int ret = wait_consider_task(wo, 0, p);
> + if (ret)
> + return ret;
> }
>
> return 0;
>
> ---
> If it was a detached task, do_wait_thread() skipped over it. In the C/R
> kernel we were setting the ->exit_signal to -1 for a "ghost" process.
> I assumed that the container-init exited without waiting for the "ghost"
> and we were getting the crash in proc_flush_mnt() when the ghost exited.
The point is that wait_consider_task() skips detached tasks as soon as they are
not ptraced. So removing the check in do_wait_thread() should not have changed
the behavior. Am I missing something?
Thanks,
Louis
--
Dr Louis Rilling Kerlabs
Skype: louis.rilling Batiment Germanium
Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes
http://www.kerlabs.com/ 35700 Rennes
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