On Sa, 2016-01-09 at 20:34 +0300, Andrey Korolyov wrote: > Hello, > > during regular operations within linux guest with USB EHCI frontend I > am seeing process crashes with an assert during regular operations > like dpkg install: > > hw/usb/dev-storage.c:334: usb_msd_handle_reset: Assertion `s->req == > ((void *)0)' failed. > > This does happen when real block backend is an USB-attached device > itself, so we are hitting some subtle race right there, because a > single change of a backend to a raw file sitting on SSD has never > triggered this block with the linux guest (but xBSD pre-reboot flush > would trigger assertion from time to time in the usb_cancel_packet() > without regarding physical backend type: > > hw/usb/core.c:508: usb_cancel_packet: Assertion > `usb_packet_is_inflight(p)' failed. > ) > > Since the 2.2.0 which I am running is not exactly freshest one, I > could re-check with master today or tomorrow, but log for hw/usb/ has > no related commits for intentional fixes over one or another issue.
Checking would be nice, but I likewise don't expect things being different on 2.5. Most likely these are bugs in rarely taken code paths, probably because the guest cancels requests and/or resets device due to timeouts (which in turn are triggered by slow backing storage on the host). Any chance you can rebuild qemu with DEBUG_MSD enabled (in hw/usb/dev-storage.c), then trigger the asserts again, so we hopefully get a useful trail of the events triggering the bugs? Kevin, is is possible to limit transfer rates for block devices, to simplify debugging stuff like this? Preferably in a way supported by libvirt? thanks, Gerd
