Messages in this thread | | | Date | Thu, 9 Oct 2008 04:44:49 -0700 | From | "Paul E. McKenney" <> | Subject | Re: RCU hang on cpu re-hotplug with 2.6.27rc8 |
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On Thu, Oct 09, 2008 at 06:56:46AM +0200, Andi Kleen wrote: > [fix up Thomas' address to not bounce] > > On Wed, Oct 08, 2008 at 06:33:21PM -0700, Paul E. McKenney wrote: > > The attached patch (similar to one in -tip, but set up for mainline and > > tweaked to make stall-checking on by default) should get you a stack > > trace of any CPUs holding up RCU grace periods for more than about > > three seconds. > > > > On the off-chance that this helps. > > It actually does. The stall detector makes the online echo return > after three seconds, although it's not 100% clear to me why.
Interesting. This behavior would be consistent with the CPU entering dyntick-idle mode without RCU's being aware of this. Except that your earlier .config file says "# CONFIG_NO_HZ is not set". And that would mean that the CPU really should be invoking RCU's state machine every scheduling tick.
I confess confusion.
Thanx, Paul
> here's the backtrace > > RCU detected CPU 14 stall (t=4295149800/5928 jiffies) > Pid: 0, comm: swapper Not tainted 2.6.27-rc9 #5 > > Call Trace: > <IRQ> [<ffffffff8025d188>] __rcu_pending+0x6e/0x1d9 > [<ffffffff8025d329>] rcu_pending+0x36/0x6e > [<ffffffff8023b480>] update_process_times+0x37/0x5b > [<ffffffff8024be72>] tick_periodic+0x68/0x74 > [<ffffffff8024be9f>] tick_handle_periodic+0x21/0x66 > [<ffffffff8021bcd2>] smp_apic_timer_interrupt+0x8a/0xa8 > [<ffffffff8020bfe6>] apic_timer_interrupt+0x66/0x70 > <EOI> [<ffffffff803adb39>] ? acpi_safe_halt+0x2b/0x3e > [<ffffffff803adbfa>] ? acpi_idle_enter_c1+0xae/0x102 > [<ffffffff804ffdd6>] ? cpuidle_idle_call+0x70/0xa2 > [<ffffffff8020a097>] ? cpu_idle+0x7e/0x9c > [<ffffffff805bef4a>] ? start_secondary+0x157/0x15c > > Timer issue? > > > -Andi
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