Comment 146 for bug 1505564

Ok, nm about the sosreport - I got the info from some older emails from axino, nova is using qemu-nbd to locally mount images and access the partitions inside them. I was able to trivially reproduce this simply by creating an image, attaching it with qemu-nbd to /dev/nbd0, partitioning it and mkfs its p1 and then mounting it, then while copying a file to it, performing qemu-nbd -d to un-attach it to /dev/nbd0. That causes the spam of "Attempted..." error messages.

So this appears to be a simple case of nova calling qemu-nbd -d while there is still I/O to the image. The right thing to do is simply ratelimit the error messages (and they really should be anyway, as they're printing directly inside a loop). The messages themselves do not indicate any kernel error, simply that the nbd device was removed while being written to.

Can you try this kernel PPA to see if it fixes the problem? You will still see the error messages, but only a few lines since they'll be ratelimited.

Of course there is still the (probably more serious) problem of the serial port driver hanging a cpu and eating up memory; that probably deserves its own bug, since it's caused by this, but a separate issue.