On Mon, 1 Feb 2021 11:33:08 +0100 Erik Skultety <eskultet@xxxxxxxxxx> wrote: > On Mon, Feb 01, 2021 at 09:48:11AM +0000, Daniel P. Berrangé wrote: > > On Mon, Feb 01, 2021 at 10:45:43AM +0100, Erik Skultety wrote: > > > On Mon, Feb 01, 2021 at 09:42:32AM +0000, Daniel P. Berrangé > > > wrote: > > > > On Fri, Jan 29, 2021 at 05:34:36PM -0600, Jonathon Jongsma > > > > wrote: > > > > > On Thu, 7 Jan 2021 17:43:54 +0100 > > > > > Erik Skultety <eskultet@xxxxxxxxxx> wrote: > > > > > > > > > > > > Tested with v6.10.0-283-g1948d4e61e. > > > > > > > > > > > > > > 1.Can define/start/destroy mdev device successfully; > > > > > > > > > > > > > > 2.'virsh nodedev-list' has no '--active' option, which is > > > > > > > inconsistent with the description in the patch： > > > > > > > # virsh nodedev-list --active > > > > > > > error: command 'nodedev-list' doesn't support option > > > > > > > --active > > > > > > > > > > > > > > 3.virsh client hang when trying to destroy a mdev device > > > > > > > which is using by a vm, and after that all 'virsh nodev*' > > > > > > > cmds will hang. If restarting llibvirtd after that, > > > > > > > libvirtd will hang. > > > > > > > > > > > > It hangs because underneath a write to the 'remove' sysfs > > > > > > attribute is now blocking for some reason and since we're > > > > > > relying on mdevctl to do it for us, hence "it hangs". I'm > > > > > > not trying to make an excuse, it's plain wrong. I'd love to > > > > > > rely on such a basic functionality, but it looks like we'll > > > > > > have to go with a extremely ugly workaround and try to get > > > > > > the list of active domains from the nodedev driver and see > > > > > > whether any of them has the device assigned before we try > > > > > > to destroy the mdev via the nodedev driver. > > > > > > > > > > So, I've been trying to figure out a way to do this, but as > > > > > far as I know, there's no way to get a list of active domains > > > > > from within the nodedev driver, and I can't think of any > > > > > better ways to handle it. Any ideas? > > > > > > > > Correct, the nodedev driver isn't permitted to talk to any of > > > > the virt drivers. > > > > > > Oh, not even via secondary connection? What makes nodedev so > > > special, since we can open a secondary connection from e.g. the > > > storage driver? > > > > It is technically possible, but it should never be done, because it > > introduces a bi-directional dependancy between the daemons which > > introduces the danger of deadlocking them. None of the secondary > > drivers should connect to the hypervisor drivers. > > > > > > Is there anything in sysfs which reports whether the device is > > > > in use ? > > > > > > Nothing that I know of, the way it used to work was that you > > > tried to write to sysfs and kernel returned a write error with > > > "device in use" or something like that, but that has changed > > > since :(. > > Without having tried this and since mdevctl is just a Bash script, > can we bypass mdevctl on destroys a little bit by constructing the > path to the sysfs attribute ourselves and perform a non-blocking > write of zero bytes to see if we get an error? If so, we'll skip > mdevctl and report an error. If we don't, we'll invoke mdevctl to > remove the device in order to remain consistent. Would that be an > acceptable workaround (provided it would work)? As far as I can tell, this doesn't work. According to my tests, attempting to write zero bytes to $(mdev_sysfs_path)/remove doesn't result in an error if the mdev is in use by a vm. It just "successfully" writes zero bytes. Adding Alex to cc in case he has an idea for a workaround here. Jonathon
