From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41836) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aJ041-0003DK-Az for qemu-devel@nongnu.org; Tue, 12 Jan 2016 09:36:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aJ03w-0000id-Bg for qemu-devel@nongnu.org; Tue, 12 Jan 2016 09:36:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39588) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aJ03w-0000iP-6V for qemu-devel@nongnu.org; Tue, 12 Jan 2016 09:36:44 -0500 Date: Tue, 12 Jan 2016 15:36:40 +0100 From: Kevin Wolf Message-ID: <20160112143640.GF4841@noname.redhat.com> References: <1452608259.29014.26.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1452608259.29014.26.camel@redhat.com> Subject: Re: [Qemu-devel] usb-storage assertions List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gerd Hoffmann Cc: hdegoede@redhat.com, Andrey Korolyov , "qemu-devel@nongnu.org" Am 12.01.2016 um 15:17 hat Gerd Hoffmann geschrieben: > 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? Yes. In the qemu command line, you can limit the rate with -drive throttling.bps_total=... and similar options (you can instead throttle based on iops instead, and you can have separate read/write limits - I don't think you need any of these, though). I have never used it in libvirt, but libvirt.org seems to suggest that it looks like this (seems to be for Xen, but you get the idea): 10000000 400000 100000 Kevin