On Fri 2015-09-04 16:49:46, Paul E. McKenney wrote: > On Fri, Sep 04, 2015 at 02:11:30PM +0200, Petr Mladek wrote: > > The deadline to force the quiescent state (jiffies_force_qs) is currently > > updated only when the previous timeout passed. But the timeout used for > > wait_event() is always the entire original timeout. This is strange. > > They tell me that kthreads aren't supposed to every catch signals, > hence the WARN_ON() in the early-exit case stray-signal case.
Yup, I have investigated this recently. All signals are really blocked for kthreads by default. There are few threads that use signals but they explicitly enable it by allow_signal(). > In the case where we were awakened with an explicit force-quiescent-state > request, we do the scan, and then wait the full time for the next scan. > So the point of the delay is to space out the scans, not to fit a > pre-determined schedule. > > The reason we get awakened with an explicit force-quiescent-state > request is that a given CPU just got inundated with RCU callbacks > or that rcutorture wants to hammer this code path. > > So I am not seeing this as anything in need of fixing. > > Am I missing something subtle here? There is the commit 88d6df612cc3c99f5 ("rcu: Prevent spurious-wakeup DoS attack on rcu_gp_kthread()"). It suggests that the spurious wakeups are possible. I would consider this patch as a fix/clean up of this Dos attack fix. Huh, I forgot to mention it in the commit message. To be honest, I personally do not know how to trigger the spurious wakeup in the current state of the code. I am trying to convert the kthread into the kthread worker API and there I got the spurious wakeups but this is another story. Thanks a lot for reviewing. Best Regards, Petr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/