Re: [PATCH] tests/functional/test_x86_64_hotplug_cpu: Fix race condition during unplug

[Daniel P . Berrangé]

On Tue, Jan 07, 2025 at 01:03:52PM +0100, Thomas Huth wrote:
> On 07/01/2025 12.57, Daniel P. Berrangé wrote:
> > On Tue, Jan 07, 2025 at 12:52:45PM +0100, Thomas Huth wrote:
> > > When unplugging the CPU, the test tries to check for a successful
> > > unplug by changing to the /sys/devices/system/cpu/cpu1 directory
> > > to see whether that fails. However, the "cd" could be faster than
> > > the unplug operation in the kernel, so there is a race condition
> > > and the test sometimes fails here.
> > > Fix it by trying to change the directory in a loop until the the
> > > CPU has really been unplugged.
> > > 
> > > Reported-by: Stefan Hajnoczi <stefanha@gmail.com>
> > > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > > ---
> > >   tests/functional/test_x86_64_hotplug_cpu.py | 6 ++++--
> > >   1 file changed, 4 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/tests/functional/test_x86_64_hotplug_cpu.py 
> > > b/tests/functional/test_x86_64_hotplug_cpu.py
> > > index b1d5156c72..7b9200ac2e 100755
> > > --- a/tests/functional/test_x86_64_hotplug_cpu.py
> > > +++ b/tests/functional/test_x86_64_hotplug_cpu.py
> > > @@ -59,11 +59,13 @@ def test_hotplug(self):
> > >                                             'cd 
> > > /sys/devices/system/cpu/cpu1',
> > >                                             'cpu1#')
> > > +        exec_command_and_wait_for_pattern(self, 'cd ..', prompt)
> > 
> > Is this actually needed ? Are we keeping the CPU from being unplugged by
> > being in that dir ? If so, why isn't it also needed in the while loop
> > below ?
> 
> I added it to make the console output less confusing (otherwise it's still
> shown in the prompt after the CPU has been unplugged)... but I can also
> remove this line again if you prefer it?

No, i'm not that fussed.


With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|