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?
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@xxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxxxxx> 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
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