Messages in this thread | | | Date | Thu, 7 Jan 2016 10:10:54 +1100 | Subject | Re: rcu_preempt self-detected stall on CPU from 4.4-rc4, since 3.17 | From | Ross Green <> |
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Just for completeness I have attached another rcu_preempt stall warning from a kinux-3.17.1 kernel.
So it looks like these stall warning go back that far.
It could be that the kernel instrumentation improved enough to detect this situation around the 3.17 kernel. I can't find any earlier records of these stall warnings before these kernels. I guess someone must have suspected there was a potential for these stalls and hence the detection facility.
Regards,
Ross
On Tue, Jan 5, 2016 at 1:21 AM, Ross Green <rgkernel@gmail.com> wrote: > Well with the release of 4.4-rc8 I have built and > started testing the kernel. > > With some luck I managed to get a rcu_preempt stall within a few hours > of testing. > > Upon booting, I ran a small series of bench marks to make sure > everything is running as expected. limited regression testing and then > just left the system to idle away, with periodic monitoring from the > network. > > > please find attached two stack traces from linux-4.4-rc8 and also linux-4.4-rc7. > > The interesting thing with the rc7 trace is that there are multiple > stalls that have occurred over a 6 day period. > > I realise Paul you have a number of changes pending for the the RCU > code. It would be good to try and establish what is happening with > these stalls before the impact of those changes given that timings and > dynamics might change whats happening in the current environment. > > As reported earlier, i have never been able to induce these stalls > with heavy loading of the system. The only method I can be sure of is > to leave the system quiet and let time go by till a stall occurs. > > Regards, > > Ross > > On Mon, Jan 4, 2016 at 9:00 AM, Ross Green <rgkernel@gmail.com> wrote: >> Thanks Paul for your analysis and investigation, >> >> I understand your patches are designed not to "fix" the problem, but >> more to move the problem ahead. >> >> I will include a few more stack traces from various kernels. I can go >> back to around 3.17, with similar trace results. >> >> My observation is that the problem can occur at various times and with >> out any "bad" effect other than more stalls could happen afterwards. >> >> At first I wondered if they might actually be a false positive as the >> kernel seemed to carry on and run quite happily. It is rare that I >> find a kernel just locks up after observing such a stall, or a >> complete kernel splat! >> >> Unfortunately with my testing I have never been able to induce the >> problem under any heavy load that would immediately trigger the >> problem. Indeed most heavy cpu utilisation seemed to just sail on >> quite nicely. >> >> The time for a fault, seems so far, to be non-deterministic with >> quiescent systems taking anywhere from a few hours through to some six >> days before showing the problem. >> >> More recent kernels seem to have richer stall and back trace >> information so I was hoping that might shed some light on how they >> might be occurring.. >> >> I usually only run a kernel till I get a new -rc release to test with, >> so a run of 1 week is a typical cycle. >> >> I just wish I could find a sure fire method to trigger the problem!! >> >> I have included a few more traces of various kernels all showing the problem. >> >> Regards, >> >> Ross >> >> On Mon, Jan 4, 2016 at 5:15 AM, Paul E. McKenney >> <paulmck@linux.vnet.ibm.com> wrote: >>> On Sun, Jan 03, 2016 at 07:27:17PM +1100, Ross Green wrote: >>>> I would not describe the load on this test machine as high or real time. >>>> >>>> Apart from a number of standard daemons not much more is running at all! >>>> >>>> I normally build a release kernel as soon as possible and set it running. >>>> Typically I run a series of benchmarks to confirm most things appear >>>> to be working and then just leave it running. During a normal day i >>>> will check on the machine 4/5 times just to see how its going! >>>> Typically I will logon remotely via wifi network connection. >>>> >>>> just for your information i will include a few other stack traces from >>>> previous kernels that may show some trend! >>>> >>>> >>>> Please see the attachments. >>> >>> Thank you for the additional details. This does look similar to some >>> problems I am seeing, though only in heavy rcutorture workloads with >>> CPU hotplugging. >>> >>> I have some crude workarounds in progress, see for example >>> 2da26818e515 (rcu: Awaken grace-period kthread when stalled) at >>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git. >>> This workaround kicks the RCU grace-period kthread on every stall warning. >>> In my testing, this workaround results in slow but real forward progress. >>> >>> I have a better workaround in progress, however, please note: >>> >>> 1. I have no intention of sending these workarounds upstream. >>> >>> 2. The workarounds will splat when they take effect. In other words, >>> the idea is not to paper over the problem, but instead to allow >>> me to separate testing concerns. >>> >>> 3. A fix is needed for the underlying bug, wherever it might be. >>> >>> Thanx, Paul >>> >>>> Regards, >>>> >>>> Ross >>>> >>>> >>>> >>>> On Sun, Jan 3, 2016 at 5:17 PM, Paul E. McKenney >>>> <paulmck@linux.vnet.ibm.com> wrote: >>>> > On Sun, Jan 03, 2016 at 04:29:11PM +1100, Ross Green wrote: >>>> >> Still seeing these rcu_preempt stalls on kernels through to 4.4-rc7 >>>> >> >>>> >> Still have not found a sure fire method to evoke this stall, but have >>>> >> found that it will normally occur within a week of running a kernel - >>>> >> usually when it is quiet with light load. >>>> >> >>>> >> Have seen similar self detected stalls all the way back to 3.17. >>>> >> Most recent kernels have included 4.4-rc5 4.4-rc6 and 4.4-rc7 >>>> >> >>>> >> Regards, >>>> >> >>>> >> Ross >>>> >> >>>> >> On Fri, Dec 11, 2015 at 10:17 PM, Ross Green <rgkernel@gmail.com> wrote: >>>> >> > I have been getting these stalls in kernels going back to 3.17. >>>> >> > >>>> >> > This stall occurs usually under light load but often requires several >>>> >> > days to show itself. I have not found any simple way to trigger the >>>> >> > stall. Indeed heavy workloads seems not to show the fault. >>>> >> > >>>> >> > Anyone have any thoughts here? >>>> >> > >>>> >> > The recent patch by peterz with kernel/sched/wait.c I thought might >>>> >> > help the situation, but alas after a few days of running 4.4-rc4 the >>>> >> > following turned up. >>>> >> > >>>> >> > [179922.003570] INFO: rcu_preempt self-detected stall on CPU >>>> >> > [179922.008178] INFO: rcu_preempt detected stalls on CPUs/tasks: >>>> >> > [179922.008178] 0-...: (1 ticks this GP) idle=a91/1/0 >>>> > >>>> > CPU 0 is non-idle from an RCU perspective. >>>> > >>>> >> > softirq=1296733/1296733 fqs=0 >>>> >> > [179922.008178] >>>> >> > [179922.008209] (detected by 1, t=8775 jiffies, g=576439, c=576438, q=102) >>>> >> > [179922.008209] Task dump for CPU 0: >>>> >> > [179922.008209] swapper/0 R [179922.008209] running [179922.008209] 0 0 0 0x00000000 >>>> >> > [179922.008209] Backtrace: >>>> >> > >>>> >> > [179922.008239] Backtrace aborted due to bad frame pointer <c0907f54> >>>> > >>>> > Can't have everything, I guess... >>>> > >>>> >> > [179922.008239] rcu_preempt kthread starved for 8775 jiffies! g576439 c576438 f0x0 s3 ->state=0x1 >>>> > >>>> > Something is keeping the rcu_preempt grace-period kthread from >>>> > running. This far into the grace period, it should have a >>>> > timer event waking it every few jiffies. It is currently >>>> > in TASK_INTERRUPTIBLE state. >>>> > >>>> >> > [179922.060302] 0-...: (1 ticks this GP) idle=a91/1/0 softirq=1296733/1296733 fqs=0 >>>> >> > [179922.068023] (t=8775 jiffies g=576439 c=576438 q=102) >>>> >> > [179922.073913] rcu_preempt kthread starved for 8775 jiffies! g576439 c576438 f0x2 s3 ->state=0x100 >>>> > >>>> > Same story, same grace period, pretty much same time. Now there is an FQS >>>> > request (f0x2) and the state is now TASK_WAKING (->state=0x100 == 256). >>>> > >>>> >> > [179922.083587] Task dump for CPU 0: >>>> >> > [179922.087097] swapper/0 R running 0 0 0 0x00000000 >>>> >> > [179922.093292] Backtrace: >>>> >> > [179922.096313] [<c0013ea8>] (dump_backtrace) from [<c00140a4>] (show_stack+0x18/0x1c) >>>> >> > [179922.104675] r7:c0908514 r6:80080193 r5:00000000 r4:c090aca8 >>>> >> > [179922.110809] [<c001408c>] (show_stack) from [<c005a858>] (sched_show_task+0xbc/0x110) >>>> >> > [179922.119049] [<c005a79c>] (sched_show_task) from [<c005ccd4>] (dump_cpu_task+0x40/0x44) >>>> >> > [179922.127624] r5:c0917680 r4:00000000 >>>> >> > [179922.131042] [<c005cc94>] (dump_cpu_task) from [<c0082268>] (rcu_dump_cpu_stacks+0x9c/0xdc) >>>> >> > [179922.140350] r5:c0917680 r4:00000001 >>>> >> > [179922.143157] [<c00821cc>] (rcu_dump_cpu_stacks) from [<c008637c>] (rcu_check_callbacks+0x504/0x8e4) >>>> >> > [179922.153808] r9:c0908514 r8:c0917680 r7:00000066 r6:2eeab000 >>>> >> > r5:c0904300 r4:ef7af300 >>>> >> > [179922.161499] [<c0085e78>] (rcu_check_callbacks) from [<c00895d0>] (update_process_times+0x40/0x6c) >>>> >> > [179922.170898] r10:c009a584 r9:00000001 r8:ef7abc4c r7:0000a3a3 >>>> >> > r6:4ec3391c r5:00000000 >>>> >> > [179922.179901] r4:c090aca8 >>>> >> > [179922.182708] [<c0089590>] (update_process_times) from [<c009a580>] >>>> >> > (tick_sched_handle+0x50/0x54) >>>> >> > [179922.192108] r5:c0907f10 r4:ef7abe40 >>>> >> > [179922.195983] [<c009a530>] (tick_sched_handle) from [<c009a5d4>] >>>> >> > (tick_sched_timer+0x50/0x94) >>>> >> > [179922.204895] [<c009a584>] (tick_sched_timer) from [<c0089fe4>] >>>> >> > (__hrtimer_run_queues+0x110/0x1a0) >>>> >> > [179922.214324] r7:00000000 r6:ef7abc40 r5:ef7abe40 r4:ef7abc00 >>>> >> > [179922.220428] [<c0089ed4>] (__hrtimer_run_queues) from [<c008a674>] >>>> >> > (hrtimer_interrupt+0xac/0x1f8) >>>> >> > [179922.227111] r10:ef7abc78 r9:ef7abc98 r8:ef7abc14 r7:ef7abcb8 >>>> >> > r6:ffffffff r5:00000003 >>>> >> > [179922.238220] r4:ef7abc00 >>>> >> > [179922.238220] [<c008a5c8>] (hrtimer_interrupt) from [<c00170ec>] >>>> >> > (twd_handler+0x38/0x48) >>>> >> > [179922.238220] r10:c09084e8 r9:fa241100 r8:00000011 r7:ef028780 >>>> >> > r6:c092574c r5:ef005cc0 >>>> > >>>> > All interrupt stack up to this point. >>>> > >>>> > It is quite possible that the stuff below here is at fault as well. >>>> > That said, the grace-period should actually get to execute at some >>>> > point. Do you have a heavy real-time load that might be starving >>>> > things? >>>> > >>>> > Thanx, Paul >>>> > >>>> >> > [179922.257110] r4:00000001 >>>> >> > [179922.257110] [<c00170b4>] (twd_handler) from [<c007c8f8>] (handle_percpu_devid_irq+0x74/0x8c) >>>> >> > [179922.269683] r5:ef005cc0 r4:ef7b1740 >>>> >> > [179922.269683] [<c007c884>] (handle_percpu_devid_irq) from [<c0078454>] (generic_handle_irq+0x2c/0x3c) >>>> >> > [179922.283233] r9:fa241100 r8:ef008000 r7:00000001 r6:00000000 >>>> >> > r5:00000000 r4:c09013e8 >>>> >> > [179922.290985] [<c0078428>] (generic_handle_irq) from [<c007872c>] (__handle_domain_irq+0x64/0xbc) >>>> >> > [179922.300842] [<c00786c8>] (__handle_domain_irq) from [<c00094c0>] >>>> >> > (gic_handle_irq+0x50/0x90) >>>> >> > [179922.303222] r9:fa241100 r8:fa240100 r7:c0907f10 r6:fa24010c >>>> >> > r5:c09087a8 r4:c0925748 >>>> >> > [179922.315216] [<c0009470>] (gic_handle_irq) from [<c0014bd4>] >>>> >> > (__irq_svc+0x54/0x90) >>>> >> > [179922.319000] Exception stack(0xc0907f10 to 0xc0907f58) >>>> >> > [179922.331542] 7f00: 00000000 >>>> >> > ef7ab390 fe600000 00000000 >>>> >> > [179922.331542] 7f20: c0906000 c090849c c0900364 c06a8124 c0907f80 >>>> >> > c0944563 c09084e8 c0907f6c >>>> >> > [179922.349029] 7f40: c0907f4c c0907f60 c00287ac c0010ba8 60080113 ffffffff >>>> >> > [179922.349029] r9:c0944563 r8:c0907f80 r7:c0907f44 r6:ffffffff >>>> >> > r5:60080113 r4:c0010ba8 >>>> >> > [179922.357116] [<c0010b80>] (arch_cpu_idle) from [<c006f034>] >>>> >> > (default_idle_call+0x28/0x34) >>>> >> > [179922.368926] [<c006f00c>] (default_idle_call) from [<c006f154>] >>>> >> > (cpu_startup_entry+0x114/0x18c) >>>> >> > [179922.368926] [<c006f040>] (cpu_startup_entry) from [<c069fc6c>] >>>> >> > (rest_init+0x90/0x94) >>>> >> > [179922.385284] r7:ffffffff r4:00000002 >>>> >> > [179922.393463] [<c069fbdc>] (rest_init) from [<c08bbcec>] >>>> >> > (start_kernel+0x370/0x37c) >>>> >> > [179922.400421] r5:c0947000 r4:00000000 >>>> >> > [179922.400421] [<c08bb97c>] (start_kernel) from [<8000807c>] (0x8000807c) >>>> >> > $ >>>> > >>>> > >>> >>> >>> [unhandled content-type:application/octet-stream] | |