linux-kernel - Re: RCU hang on cpu re-hotplug with 2.6.27rc8

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Date:	Thu, 9 Oct 2008 06:56:46 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, rjw@...k.pl, dipankar@...ibm.com,
	tglx@...utronix.de
Subject: Re: RCU hang on cpu re-hotplug with 2.6.27rc8

[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.

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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