On Fri, 7 Feb 2014 12:30:06 +0100 Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > * Steven Rostedt | 2014-02-05 11:51:25 [-0500]: > > >Ulrich Obergfell pointed out that cpu_chill() calls msleep() which is woken > >up by the ksoftirqd running the TIMER softirq. But as the cpu_chill() is > >called from softirq context, it may block the ksoftirqd() from running, in > >which case, it may never wake up the msleep() causing the deadlock. > > > >I checked the vmcore, and irq/74-qla2xxx is stuck in the msleep() call, > >running on CPU 8. The one ksoftirqd that is stuck, happens to be the one that > >runs on CPU 8, and it is blocked on a lock held by irq/74-qla2xxx. As that > >ksoftirqd is the one that will wake up irq/74-qla2xxx, and it happens to be > >blocked on a lock that irq/74-qla2xxx holds, we have our deadlock. > > could you please tell me which two locks are invovled here? > Looks to be the lock of the block softirq. I don't have the core dump anymore, but from what I could tell the ksoftirqd was blocked on the block softirq lock, where the block softirq handler did a msleep (called by the qla2xxx interrupt handler). Looking at trigger_softirq() in block/blk-softirq.c, it can do a smp_callfunction() to another cpu to run the block softirq. If that happens to be the cpu where the qla2xx irq handler is doing the block softirq and is in a middle of a msleep(), I believe the ksoftirqd will try to run the softirq. If it does that, then BOOM, it's deadlocked because the ksoftirqd will never run the timer softirq either. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
