[ovs-discuss] ovs-vswitchd get stucked on ovs_rcu revalidator quiesce

Zdenek Janda zdenek.janda at cloudevelops.com
Wed Nov 27 16:32:01 UTC 2019


Hi,
issue is also on Github at
https://github.com/openvswitch/ovs-issues/issues/175, added my comments.
Now will need help from somebody familiar with code - Openvswitch is
definitively not stable on Ubuntu Bionic and we can reproduce bug
easily, so any patching can be tested but need to figure out where to
begin - so far no clue why the thread is getting stucked and why it
unstucks after gcore dump.
Best regards
Zdenek Janda

On 27. 11. 19 12:07, Zdenek Janda wrote:
> Hi,
> it took some time to catch this, now we have detection check which
> recognizes stucked ovs and automaticaly executes gdb debug. For now, i
> have included "info threads" and "thread apply all bt full", attached is
> two files with data i got from two occurrences stucked instances of
> ovs-vswitchd.
> Let me know, how to proceed next - the issue manifestates itself several
> times a day across large number of openstack compute nodes we have, so
> we have good chance to catch and test fix.
> Best regards
> Zdenek Janda
> 
> 
> On 23. 10. 19 18:49, Ben Pfaff wrote:
>> It looks like every thread is blocking in poll() except for
>> revalidator525.  Can you give me a full backtrace for that thread?  It's
>> unusual to see a futex in an OVS backtrace and it's not obvious to me
>> where it's coming from.
>>
>> On Wed, Oct 23, 2019 at 09:56:54AM +0200, Zdenek Janda wrote:
>>> Hello,
>>> debugged on next occurence. Here is info on stucked revalidator525:
>>>
>>> Id   Target Id         Frame
>>> * 1    Thread 0x7fde892b4e00 (LWP 1499) "ovs-vswitchd"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x55a40e6d75e0, nfds=2,
>>> timeout=76638) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   2    Thread 0x7fde855a1700 (LWP 2131) "urcu4" 0x00007fde879f9bf9 in
>>> __GI___poll (fds=0x7fde40004d10, nfds=2, timeout=75817) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   3    Thread 0x7fddd1ffb700 (LWP 4596) "handler482" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddb86440e0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   4    Thread 0x7fddd27fc700 (LWP 4597) "handler483" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddd84e11e0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   5    Thread 0x7fddd2ffd700 (LWP 4598) "handler484" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddec3062d0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   6    Thread 0x7fddd37fe700 (LWP 4599) "handler485" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde341c3f80, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   7    Thread 0x7fde86da4700 (LWP 4600) "handler486" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde500e8530, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   8    Thread 0x7fde865a3700 (LWP 4601) "handler487" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddf40c00c0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   9    Thread 0x7fde85da2700 (LWP 4602) "handler488" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddfc06e480, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   10   Thread 0x7fde84da0700 (LWP 4603) "handler489" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde78049250, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   11   Thread 0x7fde73fff700 (LWP 4604) "handler490" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddc8016700, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   12   Thread 0x7fde737fe700 (LWP 4605) "handler491" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fdde800cbd0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   13   Thread 0x7fde72ffd700 (LWP 4606) "handler492" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde60012fb0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   14   Thread 0x7fde727fc700 (LWP 4607) "handler493" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde24017bb0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   15   Thread 0x7fde71ffb700 (LWP 4608) "handler494" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddd40060b0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   16   Thread 0x7fde717fa700 (LWP 4609) "handler495" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde54004ef0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   17   Thread 0x7fde70ff9700 (LWP 4610) "handler496" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde38008630, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   18   Thread 0x7fde5bfff700 (LWP 4611) "handler497" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fdda400c650, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   19   Thread 0x7fde5b7fe700 (LWP 4612) "handler498" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde14015730, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   20   Thread 0x7fde5affd700 (LWP 4614) "handler499" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde28016fc0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   21   Thread 0x7fde5a7fc700 (LWP 4615) "handler500" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddf0007570, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   22   Thread 0x7fde59ffb700 (LWP 4616) "handler501" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde04012990, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   23   Thread 0x7fde597fa700 (LWP 4617) "handler502" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddc0019910, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   24   Thread 0x7fde58ff9700 (LWP 4618) "handler503" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde3c005810, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   25   Thread 0x7fde4bfff700 (LWP 4619) "handler504" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde08005770, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   26   Thread 0x7fde4b7fe700 (LWP 4620) "handler505" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde2c0043e0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   27   Thread 0x7fde4affd700 (LWP 4621) "handler506" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde7c01c4f0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   28   Thread 0x7fde4a7fc700 (LWP 4622) "handler507" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddcc014890, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   29   Thread 0x7fde49ffb700 (LWP 4623) "handler508" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fdda8004c00, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   30   Thread 0x7fde497fa700 (LWP 4624) "handler509" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde0c006450, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   31   Thread 0x7fde48ff9700 (LWP 4625) "handler510" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde64004c40, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   32   Thread 0x7fde13fff700 (LWP 4626) "handler511" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde6c000b20, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   33   Thread 0x7fde137fe700 (LWP 4627) "handler512" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fddc400b240, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   34   Thread 0x7fde12ffd700 (LWP 4628) "handler513" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde180056c0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   35   Thread 0x7fde127fc700 (LWP 4629) "handler514" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fdde0005ea0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   36   Thread 0x7fde11ffb700 (LWP 4630) "handler515" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde00007af0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   37   Thread 0x7fde117fa700 (LWP 4631) "handler516" 0x00007fde879f9bf9
>>> in __GI___poll (fds=0x7fde6800b2d0, nfds=3, timeout=2147483647) at
>>> ../sysdeps/unix/sysv/linux/poll.c:29
>>>   38   Thread 0x7fde10ff9700 (LWP 4632) "revalidator517"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fde5c0a0960, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   39   Thread 0x7fddfbfff700 (LWP 4633) "revalidator518"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fde4c00bbc0, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   40   Thread 0x7fddfb7fe700 (LWP 4634) "revalidator519"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fddb0036600, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   41   Thread 0x7fddfaffd700 (LWP 4635) "revalidator520"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fdddc06fef0, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   42   Thread 0x7fddfa7fc700 (LWP 4636) "revalidator521"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fde800016a0, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   43   Thread 0x7fddf9ffb700 (LWP 4637) "revalidator522"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fddac07a390, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   44   Thread 0x7fddf97fa700 (LWP 4638) "revalidator523"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fde40043230, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   45   Thread 0x7fddf8ff9700 (LWP 4639) "revalidator524"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fdde4060d20, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   46   Thread 0x7fddd3fff700 (LWP 4640) "revalidator525"
>>> 0x00007fde8853237b in futex_abstimed_wait (private=<optimized out>,
>>> abstime=0x0, expected=10, futex_word=0x55a40e4afa78)
>>>     at ../sysdeps/unix/sysv/linux/futex-internal.h:172
>>>   47   Thread 0x7fddd17fa700 (LWP 4641) "revalidator526"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fde2004bd10, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   48   Thread 0x7fddd0ff9700 (LWP 4642) "revalidator527"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fddbc07be70, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   49   Thread 0x7fddb7fff700 (LWP 4643) "revalidator528"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fde1c04bd20, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>   50   Thread 0x7fddb77fe700 (LWP 4644) "revalidator529"
>>> 0x00007fde879f9bf9 in __GI___poll (fds=0x7fde30027a50, nfds=2,
>>> timeout=2147483647) at ../sysdeps/unix/sysv/linux/poll.c:29
>>>
>>>
>>>
>>> So here is the thread:
>>>  46   Thread 0x7fddd3fff700 (LWP 4640) "revalidator525"
>>> 0x00007fde8853237b in futex_abstimed_wait (private=<optimized out>,
>>> abstime=0x0, expected=10, futex_word=0x55a40e4afa78)
>>>     at ../sysdeps/unix/sysv/linux/futex-internal.h:172
>>>
>>> Any ideas what to do next ?
>>>
>>> Thanks
>>> Zdenek
>>>
>>> On 14. 10. 19 20:15, Ben Pfaff wrote:
>>>> On Mon, Oct 14, 2019 at 10:11:35AM +0200, Zdenek Janda wrote:
>>>>> Hello,
>>>>> we have really strange issue. Ovs-vswitchd  get stucked on ovs_rcu
>>>>> revalidator quiesce, reporting following to the log:
>>>>>
>>>>> 2019-10-14T05:11:18.049Z|00416|ovs_rcu|WARN|blocked 1000 ms waiting for
>>>>> revalidator518 to quiesce
>>>>> 2019-10-14T05:11:19.049Z|00417|ovs_rcu|WARN|blocked 2000 ms waiting for
>>>>> revalidator518 to quiesce
>>>>> 2019-10-14T05:11:21.049Z|00418|ovs_rcu|WARN|blocked 4000 ms waiting for
>>>> ...
>>>>> We have tried to debug this issue, and noticed while running strace or
>>>>> producing core dump will magically unstuck ovs-vswitchd and it starts
>>>>> working immediatelly:
>>>>>
>>>>> gcore `pidof ovs-vswitchd`
>>>>
>>>> The key question is, what is revalidator518 doing when it is failed to
>>>> quiesce?  If you attach with GDB and obtain a backtrace from the stuck
>>>> thread (and possibly from the other threads), it would probably provide
>>>> a clue.
>>>>
>>>> Do you have any idea about how busy OVS is when this happens?  The
>>>> revalidator threads should not take multiple seconds to do their work,
>>>> but if it happens anyway, it would probably happen when OVS was very
>>>> busy.
>>>>
>>>
> 



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