On Mon, 30 Jul 2007, Cornelia Huck wrote: > On Sat, 28 Jul 2007 11:36:42 -0400 (EDT), > Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > Can you tell whether this will ever cause a problem? Or is it known to > > be safe because whenever you call device_move(), the new parent was > > registered before the device being moved? > > Unfortunately, we can't make any assumptions in cio whether the new > parent was registered before the moving device. > > (A little background: We have each ccw_device as parent of a subchannel > as discovered during initial sense. In the case of z/VM (a hypervisor), > all subchannels are always consecutively numbered. Now the following > may happen: A dasd on subchannel 0 is detached and a new device, say a > ctc, is defined. As subchannel 0 was free from z/VMs perspective, the > ctc ccw_device now sits on subchannel 0 and the dasd ccw_device is > moved to the artificial 'defunct' subchannel. When the dasd is attached > again, z/VM will hand out the next free subchannel, which we allocate a > subchannel structure for and move the dasd ccw_device to. And here's > the case where the child is older than the parent...) As long as you never hold the device semaphores of both the parent and the child there shouldn't be any problem. Could this happen when a subchannel structure is deallocated? > While we don't do suspend/resume yet on s390, I don't want to rule it > out for the future... Thanks, Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
