Messages in this thread | | | Date | Fri, 13 May 2011 19:21:17 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 09/11] job control: reorganize wait_task_stopped() |
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Hi,
On 05/13, Tejun Heo wrote: > > On Thu, May 12, 2011 at 08:33:26PM +0200, Oleg Nesterov wrote: > > > At first glance, do_wait() does > > > > wait_task_stopped(); > > wait_task_continued(); > > > > and the state can be changed CONTINIUED -> STOPPED in between, right? > > Or something else? > > Yeah and exit transitions too.
I am not sure... but probably this depends on definition.
We already checked ->exit_state != ZOMBIE, and we are holding tasklist. The child can't exit. I mean, it can't change its ->exit_state.
However, SIGKILL can clear SIGNAL_STOP_STOPPED, and we can "miss" it. But this looks correct, the child is no longer stopped but it is still not dead. So I think in this case wait(WNOHANG | WEXITED | WSTOPPED) can fail, notabug.
OTOH, perhaps SIGKILL should set SIGNAL_STOP_CONTINUED in this case? And keep it if it was already set.
> There simply is no synchronization > there. We can probably solve it without acquiring siglock by adding > "clear this before making state transitions" flag followed by a mb()
perhaps even simpler if ->EXIT transition is fine.
Oleg.
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