On 05/14/2013 01:16 PM, Srivatsa S. Bhat wrote: > On 05/14/2013 01:08 PM, Bjørn Mork wrote: >> "Srivatsa S. Bhat" <[email protected]> writes: >>> On 05/13/2013 08:09 PM, Bjørn Mork wrote: >>> >>>> Hey, hey, hey. Turns out this wasn't that wrong after all. That merge >>>> includes a oneline diff in kernel/cpu/idle.c and it *is* actually this >>>> diff which trigger the problem for me. Reverting it, using the attached >>>> patch, makes the warning go away. Which means that it had nothing to do >>>> with your RCU changes. >>>> >>>> But I haven't the faintest idea how this is supposed to work, or even >>>> how to explain the patch properly, so I think I need some help from >>>> Thomas here. Unless this makes you understand the real issue? >>>> >>>> Thomas, why does powertop trigger the >>>> >>>> WARNING: at kernel/rcutree.c:502 rcu_eqs_exit_common.isra.48+0x3d/0x125() >>>> >>>> without the attached patch? And what is the proper resolution? >>>> >>> >>> The problem appears to be in the cpu idle poll implementation. You can >>> trigger >>> this problem by passing idle=poll in the kernel cmd-line as well, right? >> >> That sounded so obvious that it made me think "Doh, why didn't I just >> test that before?" But unfortunately there must be some other factor >> involved. No warnings observed during normal use when running with >> idle=poll: >> > > I didn't expect warnings with normal use. > >> bjorn@nemi:~$ dmesg|grep polling >> [ 0.000000] process: using polling idle threads >> >> >> I expected a flood of warnings here, but there is none until I start >> powertop (to confirm that the original issue is still there). So it's >> more than just entering cpu_idle_poll(). >> > > Yeah, of course it is :-) The warning triggers only when you enable the > tracepoint > in the idle code. And in your case, powertop does that. That's why it only > triggers when you run powertop. Alternatively, if you enable the tracepoint > yourself manually, I bet you'll see the warnings, even without using powertop. >
IOW, what I wanted to confirm with you was my theory that this problem has got nothing to do with the tick_check_broadcast_expired() check. That check only increases the probability of entering the buggy polling code during normal use (since nobody uses idle=poll in the kernel cmdline usually). That's why I requested you to try running powertop by using idle=poll, to rule out the tick_check_broadcast_expired() check from the equation. But now that you confirmed it, everything fits perfectly! Thanks a lot! Regards, Srivatsa S. Bhat -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
