[PATCH 0/6] sched/cpusets fixes, more changes are needed
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From: Oleg Nesterov on 15 Mar 2010 05:20 Ingo, Peter. Unless I missed something, with or without these patches the TASK_WAKING logic in do_fork() is very broken. - do_fork() clears PF_STARTING and then calls wake_up_new_task() which finally does s/WAKING/RUNNING. But. Nobody can take rq->lock in between. This means a signal from irq (quite possible with CLONE_THREAD) or another rt thread which preempts us can lockup. - the comment in wake_up_new_task says: We still have TASK_WAKING but PF_STARTING is gone now, meaning ->cpus_allowed is stable this is not true. Yes, nobody can take rq->lock _after_ we cleared PF_STARTING, but it is possible that another thread took this lock before and still holds it doing, say, sched_setaffinity(). No? If yes. I can make a patch, but the question is: what is the point to use TASK_WAKING in fork pathes? Can't sched_fork() set TASK_RUNNING instead? Afaics, TASK_RUNNING can equally protect from premature wakeups but doesn't these PF_STARTING complications. As for this series. Please review. I don't understand how it is possible to really test these changes. Dear cpuset developers! Please review ;) If you don't like 6/6, please make a better fix. I tried to make as "simple" patch as possible because I hardly understand cpuset.c, last time I quickly read it a long ago. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |