On Tue, 2013-04-30 at 19:09 +0200, Sebastian Andrzej Siewior wrote: > The next thing that happens is that RCU assumes nobody is doing any > progress (for almost 28secs) and triggers NMIs & printks to get some > attention. I have a trace where > - CPU0: arch_trigger_all_cpu_backtrace_handler() => printk() > has "lock" and is spinning for logbuf_lock > > - CPU1: print_cpu_stall() => printk() (spinning for the lock) => NMI => > arch_trigger_all_cpu_backtrace_handler() > it may have logbuf_lock and is spinning for "lock" > > I can't tell if CPU1 got the logbuf_lock at this time but it seemed that > it made no progress until I ended it. > This NMI releated deadlock is a problem which should also trigger > mainline, right? Well, yeah, as sending out a NMI stack dump is sorta the last resort, and is dangerous to do printks from NMI context. > > Now, the time jump on the other hand is the real issue here and is > RT-only. It looks like we get a big number of timer updates via > tick_do_update_jiffies64() because according to ktime_get() that much > time really passed by. As the NMI dump only happens because of the time jump, which as you said, is -rt only, I wouldn't say that the NMI deadlock is a mainline bug. -- 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
