I've noticed in 2.6 kernels that HIDIOCGREPORT does not wait for io
completion before returning to the caller. This creates a few unpleasant
issues for userspace:

First, code sequences such as...

        ioctl(fd, HIDIOCGREPORT, &rinfo);
        ioctl(fd, HIDIOCGUSAGE, &uinfo);
        ioctl(fd, HIDIOCGSTRING, &sdesc);

...that used to work in 2.4 now fail in 2.6 if the device takes more
than a few milliseconds to respond to HIDIOCGREPORT. (I'm seeing this
issue on APC UPSes, FWIW.)

Second, userspace code can easily flood the kernel with control messages
since the kernel provides no "backpressure". The result is a lot of
"hid-core.c: control queue full" errors and lost reports.

2.6 hid-core.c appears to submit the request and return immediately.
Although the 2.4 code differs significantly, I traced the call path to
usb-core.c, which seems to block with a timeout, so the code supports my
userspace observation. (Assuming I didn't misread it.)