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Re: [libvirt] [PATCH v3 1/2] process: wait longer on kill per assigned Hostdev





On Tue, Aug 21, 2018 at 1:15 PM Daniel P. Berrangé <berrange redhat com> wrote:
On Tue, Aug 14, 2018 at 11:27:33AM +0200, Christian Ehrhardt wrote:
> It was found that in cases with host devices virProcessKillPainfully
> might be able to send signal zero to the target PID for quite a while
> with the process already being gone from /proc/<PID>.
>
> That is due to cleanup and reset of devices which might include a
> secondary bus reset that on top of the actions taken has a 1s delay
> to let the bus settle. Due to that guests with plenty of Host devices
> could easily exceed the default timeouts.
>
> To solve that, this adds an extra delay of 2s per hostdev that is associated
> to a VM.
>
> Signed-off-by: Christian Ehrhardt <christian ehrhardt canonical com>
> ---
>  src/libvirt_private.syms |  1 +
>  src/qemu/qemu_process.c  |  5 +++--
>  src/util/virprocess.c    | 18 +++++++++++++++---
>  src/util/virprocess.h    |  1 +
>  4 files changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> index ca4a192a4a..47ea35f864 100644
> --- a/src/libvirt_private.syms
> +++ b/src/libvirt_private.syms
> @@ -2605,6 +2605,7 @@ virProcessGetPids;
>  virProcessGetStartTime;
>  virProcessKill;
>  virProcessKillPainfully;
> +virProcessKillPainfullyDelay;
>  virProcessNamespaceAvailable;
>  virProcessRunInMountNamespace;
>  virProcessSchedPolicyTypeFromString;
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index 02fdc55156..b7bf8813da 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -6814,8 +6814,9 @@ qemuProcessKill(virDomainObjPtr vm, unsigned int flags)
>          return 0;
>      }

> -    ret = virProcessKillPainfully(vm->pid,
> -                                  !!(flags & VIR_QEMU_PROCESS_KILL_FORCE));
> +    ret = virProcessKillPainfullyDelay(vm->pid,
> +                                       !!(flags & VIR_QEMU_PROCESS_KILL_FORCE),
> +                                       vm->def->nhostdevs * 2);

This API contract is a bit wierd. You've got an arbitray x2 multiplier
here...
 
Out of the discussion with Alex I derived that due to the 1 sec settling of the bus plus some extra work 2 seconds per device would be a good rule of thumb.
The delay is meant to be in seconds and here it requests 2*nhostdevs to get the amount needed.

And I'd not want to make the "unit" of the call "double-seconds" :-)

Let me add a comment at this call to explain the reasoning on the multiplier here.

> diff --git a/src/util/virprocess.c b/src/util/virprocess.c
> index ecea27a2d4..46360cc051 100644
> --- a/src/util/virprocess.c
> +++ b/src/util/virprocess.c
> @@ -341,15 +341,19 @@ int virProcessKill(pid_t pid, int sig)
>   * Returns 0 if it was killed gracefully, 1 if it
>   * was killed forcibly, -1 if it is still alive,
>   * or another error occurred.
> + *
> + * Callers can proide an extra delay to wait longer
> + * than the default.

Mention that it is in "seconds"
 
Ack

>   */
>  int
> -virProcessKillPainfully(pid_t pid, bool force)
> +virProcessKillPainfullyDelay(pid_t pid, bool force, unsigned int extradelay)
>  {
>      size_t i;
>      int ret = -1;
> +    unsigned int delay = 75 + (extradelay*5);

...and it gets another x5 multiplier here.

That *5 is due to the internal unit it polls being 0.2 seconds.
I think externally anything other than seconds (double-seconds, half-deca-seconds, ...) makes no sense.

I'll call it "polldelay" instead to make it more clear that.
That uncommon *5 ratio was there before, just not as redable (it just defined 75 in the loop header).
I'll add some text about it as well to be sure.
 
Feels nicer to just have the caller provide a x10 multiplier and
honour that directly

See above, the unit being seconds seems the most readable IMHO.
With the changes made I think it won't be as confusing.

>      const char *signame = "TERM";

> -    VIR_DEBUG("vpid=%lld force=%d", (long long)pid, force);
> +    VIR_DEBUG("vpid=%lld force=%d delay=%u", (long long)pid, force, pid);

s/pid/extradelay/
 
Yes, that was mentioned by Bjoern and queued that way.
Also in the text the delay= should be extradelay= which is ready that way.


>      /* This loop sends SIGTERM, then waits a few iterations (10 seconds)
>       * to see if it dies. If the process still hasn't exited, and
> @@ -357,9 +361,12 @@ virProcessKillPainfully(pid_t pid, bool force)
>       * wait up to 5 seconds more for the process to exit before
>       * returning.
>       *
> +     * An extra delay can be specified for cases that are expected to clean
> +     * up slower than usual.
> +     *
>       * Note that setting @force could result in dataloss for the process.
>       */
> -    for (i = 0; i < 75; i++) {
> +    for (i = 0; i < delay; i++) {
>          int signum;
>          if (i == 0) {
>              signum = SIGTERM; /* kindly suggest it should exit */
> @@ -402,6 +409,11 @@ virProcessKillPainfully(pid_t pid, bool force)
>  }


> +int virProcessKillPainfully(pid_t pid, bool force)
> +{
> +    return virProcessKillPainfullyDelay(pid, force, 0);
> +}
> +
>  #if HAVE_SCHED_GETAFFINITY

>  int virProcessSetAffinity(pid_t pid, virBitmapPtr map)
> diff --git a/src/util/virprocess.h b/src/util/virprocess.h
> index 3c5a882772..b72603ca8e 100644
> --- a/src/util/virprocess.h
> +++ b/src/util/virprocess.h
> @@ -55,6 +55,7 @@ virProcessWait(pid_t pid, int *exitstatus, bool raw)
>  int virProcessKill(pid_t pid, int sig);

>  int virProcessKillPainfully(pid_t pid, bool force);
> +int virProcessKillPainfullyDelay(pid_t pid, bool force, unsigned int);

Missing parameter name here
 
Ack, and then breaking it into new lines for 80 chars

Thanks all these will be part of a v4 ready after some syntax check and test builds ...

Regards,
Daniel
--
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--
Christian Ehrhardt
Software Engineer, Ubuntu Server
Canonical Ltd

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