From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39145) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YGyk4-0004tP-99 for qemu-devel@nongnu.org; Thu, 29 Jan 2015 18:43:21 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YGyjz-0006jr-OX for qemu-devel@nongnu.org; Thu, 29 Jan 2015 18:43:20 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48913) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YGyjz-0006jn-HG for qemu-devel@nongnu.org; Thu, 29 Jan 2015 18:43:15 -0500 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id t0TNhEFn027713 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Thu, 29 Jan 2015 18:43:14 -0500 Date: Fri, 30 Jan 2015 00:33:51 +0100 From: Kashyap Chamarthy Message-ID: <20150129233351.GD32706@tesla.redhat.com> References: <20150129162509.GA32706@tesla.redhat.com> <20150129164723.GA3860@redhat.com> <20150129172222.GC32706@tesla.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150129172222.GC32706@tesla.redhat.com> Subject: Re: [Qemu-devel] QEMU segfault: Booting an overlay with backing_file over NBD: nbd.c:nbd_receive_request():L756: read failed List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Richard W.M. Jones" Cc: qemu-devel@nongnu.org On Thu, Jan 29, 2015 at 06:22:22PM +0100, Kashyap Chamarthy wrote: > On Thu, Jan 29, 2015 at 04:47:23PM +0000, Richard W.M. Jones wrote: > > On Thu, Jan 29, 2015 at 05:25:09PM +0100, Kashyap Chamarthy wrote: [. . .] > > > On the shell where `qemu-nbd` is running, I notice this > > > > > > nbd.c:nbd_receive_request():L756: read failed > > > > > You really need to get the stack trace from that core dump to > > debug this further. > > I don't see the core dump locally (ABRT or some such not configured), > will re-test this with `gdb` in a little while to get the traces. Okay, now I had the coredump, and ran GDB ('bt full') with it[1] with qemu-debuginfo files installed. Not sure if it has inough info, as I didn't install the ~ 3.6 GB of other missing debuginfo RPMs (this is my primary laptop, I can replicate this test on a different machine with the missing debuginfo files if needed). Next, I tried the external wrapper technique you once wrote about[1], to run QEMU under `gdbserver`, here's the result: $ gdb . . . (gdb) file /usr/bin/qemu-system-x86_64 Reading symbols from /usr/bin/qemu-system-x86_64...Reading symbols from /usr/lib/debug/usr/bin/qemu-system-x86_64.debug...done. done. (gdb) target remote tcp::1234 Remote debugging using tcp::1234 Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug/usr/lib64/ld-2.20.so.debug...done. done. Loaded symbols for /lib64/ld-linux-x86-64.so.2 0x00007ffff7ddbcf0 in _start () from /lib64/ld-linux-x86-64.so.2 (gdb) cont Continuing. Program received signal SIGSEGV, Segmentation fault. 0x0000555555872159 in aio_set_fd_handler (ctx=ctx@entry=0x0, fd=8, io_read=io_read@entry=0x5555558a5470 , io_write=io_write@entry=0x5555558a4d80 , opaque=opaque@entry=0x5555562605e0) at aio-posix.c:50 Does this help? Precise steps of what I did: (1) Use the below wrapper script with `gdbserver` ---------------------------------------------------------------- $ cat /export/qemu-wrapper.sh #!/bin/bash - if ! echo "$@" | grep -sqE -- '-help|-version|-device \?' ; then gdbserver="gdbserver :1234" fi exec $gdbserver /usr/bin/qemu-system-x86_64 "$@" ---------------------------------------------------------------- (2) On shell #1, export the backing file over QEMU NBD: $ qemu-nbd -f qcow2 -p10809 \ /var/lib/libvirt/images/f21vm.qcow2 -t (3) On shell #3, Invoke the QEMU wrapper script: $ ./qemu-wrapper.sh \ -nographic \ -nodefconfig \ -nodefaults \ -m 2048 \ -device virtio-scsi-pci,id=scsi \ -device virtio-serial-pci \ -serial stdio \ -drive file=./overlay1-f21vm.qcow2,format=qcow2,if=virtio,cache=writeback Process /usr/bin/qemu-system-x86_64 created; pid = 1944 Listening on port 1234 (4) On shell #3, run GDB (output is above). [1] https://kashyapc.fedorapeople.org/virt/qemu-nbd-test/stack-traces-from-coredump.txt -- /kashyap