rcu_preempt detected stalls
Zhouyi Zhou
zhouzhouyi at gmail.com
Tue Aug 31 23:47:18 PDT 2021
Hi Neeraj
Thank you for reviewing the original logs provided by jorge and my new
test logs.
On Wed, Sep 1, 2021 at 12:08 PM Neeraj Upadhyay <neeraju at codeaurora.org> wrote:
>
> Hi,
>
> >[ 62.603086] rcu: rcu_preempt kthread starved for 5258 jiffies!
> g3017 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
> >[ 62.613246] rcu: Unless rcu_preempt kthread gets sufficient CPU
> time, OOM is now expected behavior.
>
> These logs tells us, rcu_preempt thread is in RUNNING state, however,
> the thread is not scheduled for long. So, can you please check the
> activity (scheduler traces, runqueue) on the CPU where rcu_preempt
> kthread is running (->cpu=1 in this case) , to see why rcu_preempt
> is starved of CPU cycles?
I start the qemu virtual machine with gdb remote debugging
kvm -cpu host -smp 8 -s -S -hda ./debian10.qcow2 -m 8192 -net
user,hostfwd=tcp::5556-:22,hostfwd=tcp::5555-:19 -net nic,model=e1000
-vnc :30&
gdb ./vmlinux
gdb)target remote :1234
gdb)break rcu_check_gp_kthread_starvation
gdb) continue
then rerun my second test case (2. # CONFIG_RCU_BOOST is not set)
the gdb breakpoint does not get a hit!
then I use gdb command info threads, the system seems to struggling
with memory subsystem
(gdb) info threads
Id Target Id Frame
8 Thread 8 (CPU#7 [running]) check_preemption_disabled (
what1=0xffffffff82604e07 "__this_cpu_",
what2=0xffffffff82589772 "add_return") at lib/smp_processor_id.c:14
7 Thread 7 (CPU#6 [running]) __lock_is_held (read=<optimized out>,
lock=<optimized out>) at kernel/locking/lockdep.c:5366
6 Thread 6 (CPU#5 [running]) nfsd_reply_cache_count (
shrink=0xffff88804d10fd10, sc=0xffffc9000eb4f788) at fs/nfsd/nfscache.c:295
5 Thread 5 (CPU#4 [running]) preempt_count ()
at ./arch/x86/include/asm/preempt.h:27
4 Thread 4 (CPU#3 [running]) rcu_read_lock ()
at ./include/linux/rcupdate.h:688
3 Thread 3 (CPU#2 [running]) 0xffffffff812c3b34 in find_next_bit (
offset=<optimized out>, size=<optimized out>, addr=<optimized out>)
at ./include/asm-generic/bitops/find.h:36
* 2 Thread 2 (CPU#1 [running]) do_shrink_slab (
shrinkctl=0xffffc9000031f820, shrinker=0xffff888191c2c510, priority=1)
at mm/vmscan.c:659
1 Thread 1 (CPU#0 [running]) check_wait_context (next=<optimized out>,
curr=<optimized out>) at kernel/locking/lockdep.c:4715
(gdb) bt
#0 do_shrink_slab (shrinkctl=0xffffc9000031f820, shrinker=0xffff888191c2c510,
priority=1) at mm/vmscan.c:659
#1 0xffffffff812c3c75 in shrink_slab (gfp_mask=17829066, nid=0,
memcg=0xffff888100322000, priority=1) at mm/vmscan.c:872
#2 0xffffffff812c656f in shrink_node_memcgs (sc=<optimized out>,
pgdat=<optimized out>) at mm/vmscan.c:2879
#3 shrink_node (pgdat=0xffffc9000031f820, sc=0xffffc9000031f978)
at mm/vmscan.c:2994
#4 0xffffffff812c6b9d in shrink_zones (sc=<optimized out>,
zonelist=<optimized out>) at mm/vmscan.c:3197
#5 do_try_to_free_pages (zonelist=0xffff88823fffba00, sc=0xffffc9000031f978)
at mm/vmscan.c:3252
#6 0xffffffff812c8357 in try_to_free_pages (zonelist=0xffff88823fffba00,
order=0, gfp_mask=<optimized out>, nodemask=<optimized out>)
at mm/vmscan.c:3491
#7 0xffffffff81315a9e in __perform_reclaim (ac=<optimized out>,
ac=<optimized out>, order=<optimized out>, gfp_mask=<optimized out>)
at mm/page_alloc.c:4607
#8 __alloc_pages_direct_reclaim (did_some_progress=<optimized out>,
ac=<optimized out>, alloc_flags=<optimized out>, order=<optimized out>,
gfp_mask=<optimized out>) at mm/page_alloc.c:4628
#9 __alloc_pages_slowpath (gfp_mask=3274784, order=17829066,
ac=0xffffc9000031faf8) at mm/page_alloc.c:5032
---Type <return> to continue, or q <return> to quit---
#10 0xffffffff81316b53 in __alloc_pages (gfp=17829066, order=0,
preferred_nid=<optimized out>, nodemask=0x0 <fixed_percpu_data>)
at mm/page_alloc.c:5403
#11 0xffffffff81334f13 in alloc_pages_vma (gfp=17829066, order=0,
vma=0xffff888107ed4cc0, addr=<optimized out>, node=0,
hugepage=<optimized out>) at mm/mempolicy.c:2208
#12 0xffffffff8131ee1e in __read_swap_cache_async (entry=...,
gfp_mask=17829066, vma=0x1 <fixed_percpu_data+1>, addr=0,
new_page_allocated=0x1 <fixed_percpu_data+1>) at mm/swap_state.c:459
#13 0xffffffff8131f0b8 in read_swap_cache_async (entry=...,
gfp_mask=<optimized out>, vma=<optimized out>, addr=<optimized out>,
do_poll=true) at mm/swap_state.c:525
#14 0xffffffff8131f2bd in swap_cluster_readahead (entry=...,
gfp_mask=17829066, vmf=0x6d3b4) at mm/swap_state.c:661
#15 0xffffffff8131f4c5 in swapin_readahead (entry=..., gfp_mask=2445460752,
vmf=0x1 <fixed_percpu_data+1>) at mm/swap_state.c:853
#16 0xffffffff812efcf0 in do_swap_page (vmf=0xffffc9000031fe00)
at mm/memory.c:3551
#17 0xffffffff812f3a7d in handle_pte_fault (vmf=<optimized out>)
at mm/memory.c:4562
#18 __handle_mm_fault (vma=<optimized out>, address=<optimized out>,
flags=<optimized out>) at mm/memory.c:4693
#19 0xffffffff812f4633 in handle_mm_fault (vma=0xffff888107ed4cc0,
---Type <return> to continue, or q <return> to quit---
address=140202217193320, flags=596, regs=0xffffc9000031ff58)
at mm/memory.c:4791
#20 0xffffffff8110e36e in do_user_addr_fault (regs=0xffffc9000031f820,
error_code=18446612688810460432, address=1) at arch/x86/mm/fault.c:1390
#21 0xffffffff81c13d69 in handle_page_fault (address=<optimized out>,
error_code=<optimized out>, regs=<optimized out>)
at arch/x86/mm/fault.c:1475
#22 exc_page_fault (regs=0xffffc9000031f820, error_code=18446612688810460432)
at arch/x86/mm/fault.c:1531
#23 0xffffffff81e00ace in asm_exc_page_fault ()
at ./arch/x86/include/asm/idtentry.h:568
#24 0x0000000000000016 in fixed_percpu_data ()
#25 0x0000000000000000 in ?? ()
So, I guess jorge's test may be more instructive than mine ;-)
>
>
> Thanks
> Neeraj
>
> On 9/1/2021 6:33 AM, Zhouyi Zhou wrote:
> > Hi,
> >
> > I perform following two new rounds of experiments:
> >
> >
> > Test environment (x86_64 debian10 virtual machine: kvm -cpu host -smp
> > 8 -hda ./debian10.qcow2 -m 4096 -net
> > user,hostfwd=tcp::5556-:22,hostfwd=tcp::5555-:19 -net nic,model=e1000
> > -vnc :30)
> >
> > 1. CONFIG_RCU_BOOST=y
> > 1.1 as root, run #stress-ng --sequential 100 --class scheduler -t 5m --times
> > 1.2 as regular user at the same time, run $stress-ng --sequential 100
> > --class scheduler -t 5m --times
> >
> > System begin OOM kill after 6 minutes:
> > 31 19:41:12 debian kernel: [ 847.171884] task:kworker/1:0 state:D
> > stack: 0 pid: 1634 ppid: 2 flag\
> > s:0x00004000
> > Aug 31 19:41:12 debian kernel: [ 847.171890] Workqueue: ipv6_addrconf
> > addrconf_verify_work
> > Aug 31 19:41:12 debian kernel: [ 847.171897] Call Trace:
> > Aug 31 19:41:12 debian kernel: [ 847.171903] __schedule+0x368/0xa40
> > Aug 31 19:41:12 debian kernel: [ 847.171915] schedule+0x44/0xe0
> > Aug 31 19:41:12 debian kernel: [ 847.171921]
> > schedule_preempt_disabled+0x14/0x20
> > Aug 31 19:41:12 debian kernel: [ 847.171924] __mutex_lock+0x4b1/0xa10
> > Aug 31 19:41:12 debian kernel: [ 847.171935] ? addrconf_verify_work+0xa/0x20
> > Aug 31 19:41:12 debian kernel: [ 847.171948] ? addrconf_verify_work+0xa/0x20
> > Aug 31 19:41:12 debian kernel: [ 847.171951] addrconf_verify_work+0xa/0x20
> > Aug 31 19:41:12 debian kernel: [ 847.171955] process_one_work+0x1fa/0x5b0
> > Aug 31 19:41:12 debian kernel: [ 847.171967] worker_thread+0x64/0x3d0
> > Aug 31 19:41:12 debian kernel: [ 847.171974] ? process_one_work+0x5b0/0x5b0
> > Aug 31 19:41:12 debian kernel: [ 847.171978] kthread+0x131/0x180
> > Aug 31 19:41:12 debian kernel: [ 847.171982] ? set_kthread_struct+0x40/0x40
> > Aug 31 19:41:12 debian kernel: [ 847.171989] ret_from_fork+0x1f/0x30
> > Aug 31 19:41:12 debian kernel: [ 847.176007]
> > Aug 31 19:41:12 debian kernel: [ 847.176007] Showing all locks held
> > in the system:
> > Aug 31 19:41:12 debian kernel: [ 847.176016] 1 lock held by khungtaskd/56:
> > Aug 31 19:41:12 debian kernel: [ 847.176018] #0: ffffffff82918b60
> > (rcu_read_lock){....}-{1:2}, at: debug_show_a\
> > ll_locks+0xe/0x1a0
> >
> > 2. # CONFIG_RCU_BOOST is not set
> > 2.1 as root, run #stress-ng --sequential 100 --class scheduler -t 5m --times
> > 2.2 as regular user at the same time, run $stress-ng --sequential 100
> > --class scheduler -t 5m --times
> > System begin OOM kill after 6 minutes:
> > The system is so dead, that I can't save the backtrace to file nor did
> > kernel has a chance to save the log to /var/log/messages
> >
> > Thanks
> > Zhouyi
> >
> > On Wed, Sep 1, 2021 at 1:11 AM Zhouyi Zhou <zhouzhouyi at gmail.com> wrote:
> >>
> >> followings are some of my kernel config options:
> >> CONFIG_PREEMPT=y
> >> CONFIG_PREEMPT_COUNT=y
> >> CONFIG_PREEMPTION=y
> >> CONFIG_PREEMPT_DYNAMIC=y
> >> CONFIG_PREEMPT_RCU=y
> >> CONFIG_HAVE_PREEMPT_DYNAMIC=y
> >> CONFIG_TREE_RCU=y
> >> CONFIG_PREEMPT_RCU=y
> >> CONFIG_RCU_EXPERT=y
> >> CONFIG_SRCU=y
> >> CONFIG_TREE_SRCU=y
> >> CONFIG_TASKS_RCU_GENERIC=y
> >> CONFIG_TASKS_RCU=y
> >> CONFIG_TASKS_RUDE_RCU=y
> >> CONFIG_TASKS_TRACE_RCU=y
> >> CONFIG_RCU_STALL_COMMON=y
> >> CONFIG_RCU_NEED_SEGCBLIST=y
> >> CONFIG_RCU_FANOUT=64
> >> CONFIG_RCU_FANOUT_LEAF=16
> >> # CONFIG_RCU_FAST_NO_HZ is not set
> >> # CONFIG_RCU_BOOST is not set
> >> CONFIG_RCU_NOCB_CPU=y
> >> # CONFIG_TASKS_TRACE_RCU_READ_MB is not set
> >> # end of RCU Subsystem
> >> CONFIG_MMU_GATHER_RCU_TABLE_FREE=y
> >> CONFIG_LOCKDEP_CIRCULAR_QUEUE_BITS=12
> >> # RCU Debugging
> >> CONFIG_PROVE_RCU=y
> >> # CONFIG_PROVE_RCU_LIST is not set
> >> # CONFIG_RCU_SCALE_TEST is not set
> >> CONFIG_RCU_TORTURE_TEST=m
> >> # CONFIG_RCU_REF_SCALE_TEST is not set
> >> CONFIG_RCU_CPU_STALL_TIMEOUT=21
> >> # CONFIG_RCU_TRACE is not set
> >> # CONFIG_RCU_EQS_DEBUG is not set
> >>
> >> Thanks
> >> Zhouyi
> >>
> >> On Wed, Sep 1, 2021 at 1:01 AM Zhouyi Zhou <zhouzhouyi at gmail.com> wrote:
> >>>
> >>> I did an experiment just now on x86_64 virtual machines, rcu did not
> >>> complain after 10 minutes's test, I hope my effort can provide some
> >>> clue.
> >>>
> >>> 1. I clone the fresh new linux kernel (git clone
> >>> https://kernel.source.codeaurora.cn/pub/scm/linux/kernel/git/torvalds/linux.git)
> >>> 2. compile the kernel without CONFIG_RCU_BOOST (: # CONFIG_RCU_BOOST is not set)
> >>> 3. boot the kernel on a x86_64 VM (kvm -cpu host -smp 16 -hda
> >>> ./debian10.qcow2 -m 4096 -net
> >>> user,hostfwd=tcp::5556-:22,hostfwd=tcp::5555-:19 -net nic,model=e1000
> >>> -vnc :30)
> >>> 4. run the test (stress-ng --sequential 16 --class scheduler -t 5m --times)
> >>> 5. monitor the system by constantly typing top and dmesg
> >>> 6. after 10 minutes, nothing else happens except that the dmesg report
> >>> following two messages
> >>> [ 672.528192] sched: DL replenish lagged too much
> >>> [ 751.127790] hrtimer: interrupt took 12143 ns
> >>>
> >>> So, I guess CONFIG_RCU_BOOST is not necessary for x86_64 virtual machines
> >>>
> >>> Zhouyi
> >>>
> >>> On Tue, Aug 31, 2021 at 11:24 PM Jorge Ramirez-Ortiz, Foundries
> >>> <jorge at foundries.io> wrote:
> >>>>
> >>>> Hi
> >>>>
> >>>> When enabling CONFIG_PREEMPT and running the stress-ng scheduler class
> >>>> tests on arm64 (xilinx zynqmp and imx imx8mm SoCs) we are observing the following.
> >>>>
> >>>> [ 62.578917] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> >>>> [ 62.585015] (detected by 0, t=5253 jiffies, g=3017, q=2972)
> >>>> [ 62.590663] rcu: All QSes seen, last rcu_preempt kthread activity 5254 (4294907943-4294902689), jiffies_till_next_fqs=1, root
> >>>> +->qsmask 0x0
> >>>> [ 62.603086] rcu: rcu_preempt kthread starved for 5258 jiffies! g3017 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
> >>>> [ 62.613246] rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
> >>>> [ 62.622359] rcu: RCU grace-period kthread stack dump:
> >>>> [ 62.627395] task:rcu_preempt state:R running task stack: 0 pid: 14 ppid: 2 flags:0x00000028
> >>>> [ 62.637308] Call trace:
> >>>> [ 62.639748] __switch_to+0x11c/0x190
> >>>> [ 62.643319] __schedule+0x3b8/0x8d8
> >>>> [ 62.646796] schedule+0x4c/0x108
> >>>> [ 62.650018] schedule_timeout+0x1ac/0x358
> >>>> [ 62.654021] rcu_gp_kthread+0x6a8/0x12b8
> >>>> [ 62.657933] kthread+0x14c/0x158
> >>>> [ 62.661153] ret_from_fork+0x10/0x18
> >>>> [ 62.682919] BUG: scheduling while atomic: stress-ng-hrtim/831/0x00000002
> >>>> [ 62.689604] Preemption disabled at:
> >>>> [ 62.689614] [<ffffffc010059418>] irq_enter_rcu+0x30/0x58
> >>>> [ 62.698393] CPU: 0 PID: 831 Comm: stress-ng-hrtim Not tainted 5.10.42+ #5
> >>>> [ 62.706296] Hardware name: Zynqmp new (DT)
> >>>> [ 62.710115] Call trace:
> >>>> [ 62.712548] dump_backtrace+0x0/0x240
> >>>> [ 62.716202] show_stack+0x2c/0x38
> >>>> [ 62.719510] dump_stack+0xcc/0x104
> >>>> [ 62.722904] __schedule_bug+0x78/0xc8
> >>>> [ 62.726556] __schedule+0x70c/0x8d8
> >>>> [ 62.730037] schedule+0x4c/0x108
> >>>> [ 62.733259] do_notify_resume+0x224/0x5d8
> >>>> [ 62.737259] work_pending+0xc/0x2a4
> >>>>
> >>>> The error results in OOM eventually.
> >>>>
> >>>> RCU priority boosting does work around this issue but it seems to me
> >>>> a workaround more than a fix (otherwise boosting would be enabled
> >>>> by CONFIG_PREEMPT for arm64 I guess?).
> >>>>
> >>>> The question is: is this an arm64 bug that should be investigated? or
> >>>> is this some known corner case of running stress-ng that is already
> >>>> understood?
> >>>>
> >>>> thanks
> >>>> Jorge
> >>>>
> >>>>
> >>>>
>
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
> member of the Code Aurora Forum, hosted by The Linux Foundation
Thanks
Zhouyi
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