Messages in this thread |  | | Date | Mon, 16 Feb 2015 16:05:05 -0600 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 1/3] sched: add sched_task_call() |
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On Mon, Feb 16, 2015 at 09:44:36PM +0100, Peter Zijlstra wrote: > On Mon, Feb 16, 2015 at 12:52:34PM -0600, Josh Poimboeuf wrote: > > +++ b/kernel/sched/core.c > > @@ -1338,6 +1338,23 @@ void kick_process(struct task_struct *p) > > EXPORT_SYMBOL_GPL(kick_process); > > #endif /* CONFIG_SMP */ > > > > +/*** > > + * sched_task_call - call a function with a task's state locked > > + * > > + * The task is guaranteed to remain either active or inactive during the > > + * function call. > > + */ > > +void sched_task_call(sched_task_call_func_t func, struct task_struct *p, > > + void *data) > > +{ > > + unsigned long flags; > > + struct rq *rq; > > + > > + rq = task_rq_lock(p, &flags); > > + func(p, data); > > + task_rq_unlock(rq, p, &flags); > > +} > > Yeah, I think not. We're so not going to allow running random code under > rq->lock and p->pi_lock.
Yeah, I can understand that. I definitely want to avoid touching the scheduler code. Basically I'm trying to find a way to atomically do the following:
if (task is sleeping) { walk the stack if (certain set of functions isn't on the stack) set (or clear) a thread flag for the task }
Any ideas on how I can achieve that? So far my ideas are:
1. Use task_rq_lock() -- but rq_lock is internal to sched code.
2. Use wait_task_inactive() -- I could call it twice, with the stack checking in between, and use ncsw to ensure that it didn't reschedule in the mean time. But this still seems racy. i.e., I think the task could start running after the second call to wait_task_inactive() returns but before setting the thread flag. Not sure if that's a realistic race condition or not.
3. Use set_cpus_allowed() to temporarily pin the task to its current CPU, and then call smp_call_function_single() to run the above critical section on that CPU. I'm not sure if there's a race-free way to do it but it's a lot more disruptive than I'd like...
Any ideas or guidance would be greatly appreciated!
-- Josh
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