I'm at a loss to think of what to check next. I'm thinking maybe monitoring several dozen sysfs attributes all at once, dumping them all as fast as possible might not be something sysfs was designed for, but the system doesn't appear to be giving me any indication that there is a problem with that, and my driver seems to have no trouble keeping up with the constant onslaught of sysfs "show" calls, while still managing to not skip a beat with the character devices (the data all looks good throughout).