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Message-ID: <0D818C7A2259ED42912C1E04120FDE26712E3DF3@ORSMSX111.amr.corp.intel.com> Date: Tue, 22 Mar 2016 21:04:47 +0000 From: "Chatre, Reinette" <reinette.chatre@...el.com> To: "paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com> CC: Jacob Pan <jacob.jun.pan@...ux.intel.com>, Josh Triplett <josh@...htriplett.org>, Ross Green <rgkernel@...il.com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, John Stultz <john.stultz@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, "Lai Jiangshan" <jiangshanlai@...il.com>, "dipankar@...ibm.com" <dipankar@...ibm.com>, Andrew Morton <akpm@...ux-foundation.org>, rostedt <rostedt@...dmis.org>, David Howells <dhowells@...hat.com>, Eric Dumazet <edumazet@...gle.com>, Darren Hart <dvhart@...ux.intel.com>, Frédéric Weisbecker <fweisbec@...il.com>, Oleg Nesterov <oleg@...hat.com>, pranith kumar <bobby.prani@...il.com> Subject: RE: rcu_preempt self-detected stall on CPU from 4.5-rc3, since 3.17 Hi Paul, On 2016-03-22, Paul E. McKenney wrote: > On Tue, Mar 22, 2016 at 04:35:32PM +0000, Chatre, Reinette wrote: >> On 2016-03-21, Paul E. McKenney wrote: >>> On Mon, Mar 21, 2016 at 09:22:30AM -0700, Jacob Pan wrote: >>>> On Fri, 18 Mar 2016 16:56:41 -0700 >>>> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote: >>>>> On Fri, Mar 18, 2016 at 02:00:11PM -0700, Josh Triplett wrote: >>>>>> On Thu, Feb 25, 2016 at 04:56:38PM -0800, Paul E. McKenney wrote: >>> >>> [ . . . ] >>> >>>>>> We're seeing a similar stall (~60 seconds) on an x86 development >>>>>> system here. Any luck tracking down the cause of this? If not, any >>>>>> suggestions for traces that might be helpful? >>>>> >>>>> The dmesg containing the stall, the kernel version, and the .config >>>>> would be helpful! Working on a torture test specific to this bug... > > And thank you for the .config. Your kenrle version looks to be 4.5.0. > >>>> +Reinette, she has the system that can reproduce the issue. I >>>> believe she is having some other problems with it at the moment. But >>>> the .config should be available. Version is v4.5. >>> >>> A couple of additional questions: >>> >>> 1. Is the test running on bare metal or virtualized? If the >>> latter, what is the host? >> >> Bare metal. > > OK, you are ahead of me. Mine is virtualized. > >>> 2. Does the workload involve CPU hotplug? >> >> No. > > Again, you are ahead of me. Mine makes extremely heavy use of CPU hotplug. > >>> 3. Are you seeing things like this in dmesg? >>> >>> "rcu_preempt kthread starved for 21033 jiffies" >>> "rcu_sched kthread starved for 32103 jiffies" >>> "rcu_bh kthread starved for 84031 jiffies" >>> >>> If not, you are probably facing some other bug, and should >>> proceed debugging as described in Documentation/RCU/stallwarn.txt. >> >> Below is a sample of what I see as captured with v4.5. The kernel >> configuration is attached. >> >> [ 135.456197] INFO: rcu_preempt detected stalls on CPUs/tasks: [ >> 135.457729] 3-...: (0 ticks this GP) idle=722/0/0 softirq=5532/5532 >> fqs=0 [ 135.459604] (detected by 2, t=60004 jiffies, g=2105, c=2104, >> q=165) [ 135.461318] Task dump for CPU 3: [ 135.461321] swapper/3 >> R running task 0 0 1 0x00200000 [ 135.461325] >> 00000078560040e5 ffff88017846fed0 ffffffff818af2cc ffff880100000000 [ >> 135.461330] 0000000600000003 ffff880178470000 ffff880072f32200 >> ffffffff822dcec0 [ 135.461334] ffff88017846c000 ffff88017846c000 >> ffff88017846fee0 ffffffff818af517 [ 135.461338] Call Trace: [ >> 135.461345] [<ffffffff818af2cc>] ? cpuidle_enter_state+0xfc/0x310 [ >> 135.461349] [<ffffffff818af517>] ? cpuidle_enter+0x17/0x20 [ >> 135.461353] [<ffffffff811515aa>] ? call_cpuidle+0x2a/0x40 [ >> 135.461355] [<ffffffff8115197d>] ? cpu_startup_entry+0x28d/0x360 [ >> 135.461360] [<ffffffff8108c874>] ? start_secondary+0x114/0x140 [ >> 135.461365] rcu_preempt kthread starved for 60004 jiffies! g2105 c2104 > f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1 > > And yes, it looks like you are seeing the same bug that I am tracing. > > The kthread is blocked on a schedule_timeout_interruptible(). Given > default configuration, this would have a three-jiffy timeout. > > You set CONFIG_RCU_CPU_STALL_TIMEOUT=60, which matches the 60004 jiffies > above. Is that value due to a distro setting or something? Mainline > uses CONFIG_RCU_CPU_STALL_TIMEOUT=21. Indeed ... this value originated from a Fedora configuration. >> [ 135.463965] rcu_preempt S ffff88017844fd68 0 7 2 >> 0x00000000 [ 135.463969] ffff88017844fd68 ffff88017dd8cc80 >> ffff880177ff0000 ffff880178443b80 [ 135.463973] ffff880178450000 >> ffff88017844fda0 ffff88017dd8cc80 ffff88017dd8cc80 [ 135.463977] >> 0000000000000003 ffff88017844fd80 ffffffff81ab031f 0000000100031504 [ >> 135.463981] Call Trace: [ 135.463986] [<ffffffff81ab031f>] >> schedule+0x3f/0xa0 [ 135.463989] [<ffffffff81ab42d7>] >> schedule_timeout+0x127/0x270 [ 135.463993] [<ffffffff81171a50>] ? >> detach_if_pending+0x120/0x120 [ 135.463997] [<ffffffff8116da5d>] >> rcu_gp_kthread+0x6bd/0xa30 [ 135.464000] [<ffffffff81151390>] ? >> wake_atomic_t_function+0x70/0x70 [ 135.464003] [<ffffffff8116d3a0>] ? >> force_qs_rnp+0x1b0/0x1b0 [ 135.464006] [<ffffffff8112f846>] >> kthread+0xe6/0x100 [ 135.464009] [<ffffffff8112f760>] ? >> kthread_worker_fn+0x190/0x190 [ 135.464012] [<ffffffff81ab5c0f>] >> ret_from_fork+0x3f/0x70 [ 135.464015] [<ffffffff8112f760>] ? >> kthread_worker_fn+0x190/0x190 > > How long does it take to reproduce this? If it reproduces in minutes > or hours, could you please boot with the following on the kernel command > line and dump the trace buffer shortly after the stall? > > ftrace trace_event=sched_waking,sched_wakeup,sched_wake_idle_without_ipi The trace I provided above appeared after a few minutes and not again. On previous occasions I had to wait a few hours. I tried running with the above added to the kernel command line but I have not seen the trace yet. I will leave the system overnight but then may risk not capturing the data you need so ... > If dumping manually shortly after the stall is at all non-trivial > (for example, if your reproduction time is many minute or hours), > I can supply some patches that automate this. Or you can pick > them up from -rcu: ... could you please point me to the patches you refer to? Or would you like me to try with the entire kernel from rcu/dev? > > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git > > Branch rcu/dev has these patches (and much else besides). > > Thanx, Paul > > PS: In case you are curious, when I enable those tracepoints, it > shows me that the timer is firing every three jiffies, as it > should, but that something happens between the sched_waking > and the IPI handler that should actually do the wakeup. > However, adding the traces significantly slows reproduction, > so I am writing a stress test specific to this bug to try to > speed things up, hopefully allowing more tracing to be added > while still retaining non-geologic reproduction times. Thank you very much for these details. Reinette
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