Re: [PATCH] util: retry open() when it gets interrupted by a signal

[Philipp Reisner]

Hi Daniel,

> > > > The experienced logfile entry is:
> > > >
> > > > qemu-system-x86_64: -device 
> > > > virtio-blk-pci,bus=pci.0,addr=0x7,drive=libvirt-2-format,id=virtio-disk0,bootindex=2,write-cache=on,serial=1b990c4d13b74a4e90ea:
> > > >  Could not open '/dev/drbd1003': Interrupted system call
>
> What is the actual signal you are seeing that impacts QEMU
> in this way ?
>

I do not know at this point. This only reproduces on a customer's
system we do not have access to. We do not see it in our in-house lab.
And qemu is called through libvirt through ApacheCloudStack. And it
affects only about 10%-20% of the VM start operations.

I will wrap my head around bpftrace and see if I can instruct the
customer to run that on his systems. So, maybe I can answer the
question regarding the signal in a few days. Maybe next week.

The backing device we use (drbd) does an "auto promote" action in its
open implementation. That involves exchanging some packets with some
peers on the local network. I guess that takes between 1ms to 10ms.
So, it exposes a larger time window than other backing block devices,
which probably have a shorter running open implementation.

So this is why we see it sometimes.

with regards,
 Philipp