[PATCH 00/10] resolve hangs/crashes on libvirtd shutdown

[Daniel Henrique Barboza]

As far as code goes:


Reviewed-by: Daniel Henrique Barboza <danielhb413 at gmail.com>


About the design I have a question about the timeout. Patch 5/10 is setting a
15 second timeout. How did you reach this value? Reading the bug, specially
this comment from Daniel:

https://bugzilla.redhat.com/show_bug.cgi?id=1828207#c6

He mentions "give it 5 seconds of running before shutting it down".

5 seconds before shutdown is something that most users can be slightly annoyed
but in the end don't mind that much, but 15 seconds is something that will
cause bugs to be opened because "Libvirt is taking too long to shutdown".
Besides, it's a fair assumption that a transaction that takes more than
5 or so seconds to finish is already compromised* - might as well shutdown
the daemon and deal with the errors.



* assuming user discretion to avoid shutting down the daemon in the middle
of a long duration transaction, of course.


Thanks,


DHB


On 7/14/20 6:32 AM, Nikolay Shirokovskiy wrote:
> This series follows [1] but address the issue slightly differently.
> Instead of polling for RPC thread pool termination it waits for
> thread pool drain in distinct thread and then signal the main loop
> to exit.
> 
> The series introduces new driver's methods stateShutdown/stateShutdownWait
> to finish all driver's background threads. The methods however are only
> implemented for qemu driver and only partially. There are other drivers
> that have background threads and I don't check every one of them in
> terms of how they manage their background threads.
> 
> For example node driver creates 2 threads. One of them is supposed to live
> a for a short amount of time and thus not tracked. This thread can cause issues
> on shutdown. The second thread is tracked and finished synchronously on driver
> cleanup. So this thread can not cause crashes but can cause hangs theoretically
> speaking so we may want to move the thread finishing to stateShutdownWait
> method so that possible hang will be handled by shutdown timeout.
> 
> The qemu driver also has untracked threads and they can cause crashes on
> shutdown. For example reconnect threads or reboot thread. These need to be
> tracked.
> 
> I'm going to address these issues in qemu and other drivers once the overall
> approach will be approved.
> 
> I added 2 new driver's methods so that thread finishing will be done in
> parallel. If we have only one method then the shutdown is done one by one
> effectively.
> 
> I've added clean shutdown timeout in event loop as suggested by Daniel in [2].
> Now I think why we can't just go with systemd unit management? Systemd will
> eventually send SIGKILL and we can tune the timeout using TimeoutStopUSec
> parameter. This way we even don't need to introduce new driver's methods.
> Driver's background threads can be finished in stateCleanup method. AFAIU as
> drivers are cleaned up in reverse order it is safe in the sense that already
> cleaned up driver can not be used by background threads of not yet cleaned up
> driver. Of course this way the cleanup is not done in parallel. Well to
> turn it into parallel we can introduce just stateShutdown which we don't need
> to call in netdaemon code and thus don't introduce undesired dependency of
> netdaemon on drivers concept.
> 
> [1] Resolve libvirtd hang on termination with connected long running client
>      https://www.redhat.com/archives/libvir-list/2018-July/msg00382.html
> [2] Races / crashes in shutdown of libvirtd daemon
>      https://www.redhat.com/archives/libvir-list/2020-April/msg01328.html
> 
> Nikolay Shirokovskiy (10):
>    libvirt: add stateShutdown/stateShutdownWait to drivers
>    util: always initialize priority condition
>    util: add stop/drain functions to thread pool
>    rpc: don't unref service ref on socket behalf twice
>    rpc: finish all threads before exiting main loop
>    vireventthread: add virEventThreadClose
>    qemu: exit thread synchronously in qemuDomainObjStopWorker
>    qemu: implement driver's shutdown/shutdown wait methods
>    rpc: cleanup virNetDaemonClose method
>    util: remove unused virThreadPoolNew macro
> 
>   scripts/check-drivername.py   |  2 +
>   src/driver-state.h            |  8 ++++
>   src/libvirt.c                 | 42 +++++++++++++++++++
>   src/libvirt_internal.h        |  2 +
>   src/libvirt_private.syms      |  3 ++
>   src/libvirt_remote.syms       |  1 -
>   src/qemu/qemu_domain.c        |  1 +
>   src/qemu/qemu_driver.c        | 32 +++++++++++++++
>   src/remote/remote_daemon.c    |  3 --
>   src/rpc/virnetdaemon.c        | 95 ++++++++++++++++++++++++++++++++++++-------
>   src/rpc/virnetdaemon.h        |  2 -
>   src/rpc/virnetserver.c        |  8 ++++
>   src/rpc/virnetserver.h        |  1 +
>   src/rpc/virnetserverservice.c |  1 -
>   src/util/vireventthread.c     |  9 ++++
>   src/util/vireventthread.h     |  1 +
>   src/util/virthreadpool.c      | 65 ++++++++++++++++++++---------
>   src/util/virthreadpool.h      |  6 +--
>   18 files changed, 238 insertions(+), 44 deletions(-)
>