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

Wed Oct 23 16:49:27 UTC 2019

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.
> > 
> 