Since commit d4c19cdeeb ("virtio-serial:
add missing virtio_detach_element() call") the following commands may
cause QEMU to segfault:
$ qemu -M accel=kvm -cpu host -m 1G \
-drive if=virtio,file=test.img,format=raw \
-device virtio-serial-pci,id=virtio-serial0 \
-chardev socket,id=channel1,path=/tmp/chardev.sock,server,nowait \
-device virtserialport,chardev=channel1,bus=virtio-serial0.0,id=port1
$ nc -U /tmp/chardev.sock
^C
(guest)$ cat /dev/zero >/dev/vport0p1
The segfault is non-deterministic: if the event loop notices the socket
has been closed then there is no crash. The disconnect has to happen
right before QEMU attempts to write data to the socket.
The backtrace is as follows:
Thread 1 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
0x00005555557e0698 in do_flush_queued_data (port=0x5555582cedf0, vq=0x7fffcc854290, vdev=0x55555807b1d0) at hw/char/virtio-serial-bus.c:180
180 for (i = port->iov_idx; i < port->elem->out_num; i++) {
#1 0x000055555580d363 in virtio_queue_notify_vq (vq=0x7fffcc854290) at hw/virtio/virtio.c:1524
#2 0x000055555580d363 in virtio_queue_host_notifier_read (n=0x7fffcc8542f8) at hw/virtio/virtio.c:2430
#3 0x0000555555b3482c in aio_dispatch_handlers (ctx=ctx@entry=0x5555566b8c80) at util/aio-posix.c:399
#4 0x0000555555b350d8 in aio_dispatch (ctx=0x5555566b8c80) at util/aio-posix.c:430
#5 0x0000555555b3212e in aio_ctx_dispatch (source=<optimized out>, callback=<optimized out>, user_data=<optimized out>) at util/async.c:261
#6 0x00007fffde71de52 in g_main_context_dispatch () at /lib64/libglib-2.0.so.0
#7 0x0000555555b34353 in glib_pollfds_poll () at util/main-loop.c:213
#8 0x0000555555b34353 in os_host_main_loop_wait (timeout=<optimized out>) at util/main-loop.c:261
#9 0x0000555555b34353 in main_loop_wait (nonblocking=<optimized out>) at util/main-loop.c:517
#10 0x0000555555773207 in main_loop () at vl.c:1917
#11 0x0000555555773207 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4751
The do_flush_queued_data() function does not anticipate chardev close
events during vsc->have_data(). It expects port->elem to remain
non-NULL for the duration its for loop.
The fix is simply to return from do_flush_queued_data() if the port
closes because the close event already frees port->elem and drains the
virtqueue - there is nothing left for do_flush_queued_data() to do.
Reported-by: Sitong Liu <siliu@redhat.com>
Reported-by: Min Deng <mdeng@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
QEMU README
===========
QEMU is a generic and open source machine & userspace emulator and
virtualizer.
QEMU is capable of emulating a complete machine in software without any
need for hardware virtualization support. By using dynamic translation,
it achieves very good performance. QEMU can also integrate with the Xen
and KVM hypervisors to provide emulated hardware while allowing the
hypervisor to manage the CPU. With hypervisor support, QEMU can achieve
near native performance for CPUs. When QEMU emulates CPUs directly it is
capable of running operating systems made for one machine (e.g. an ARMv7
board) on a different machine (e.g. an x86_64 PC board).
QEMU is also capable of providing userspace API virtualization for Linux
and BSD kernel interfaces. This allows binaries compiled against one
architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a
different architecture ABI (e.g. the Linux x86_64 ABI). This does not
involve any hardware emulation, simply CPU and syscall emulation.
QEMU aims to fit into a variety of use cases. It can be invoked directly
by users wishing to have full control over its behaviour and settings.
It also aims to facilitate integration into higher level management
layers, by providing a stable command line interface and monitor API.
It is commonly invoked indirectly via the libvirt library when using
open source applications such as oVirt, OpenStack and virt-manager.
QEMU as a whole is released under the GNU General Public License,
version 2. For full licensing details, consult the LICENSE file.
Building
========
QEMU is multi-platform software intended to be buildable on all modern
Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety
of other UNIX targets. The simple steps to build QEMU are:
mkdir build
cd build
../configure
make
Additional information can also be found online via the QEMU website:
http://qemu-project.org/Hosts/Linux
http://qemu-project.org/Hosts/Mac
http://qemu-project.org/Hosts/W32
Submitting patches
==================
The QEMU source code is maintained under the GIT version control system.
git clone git://git.qemu-project.org/qemu.git
When submitting patches, the preferred approach is to use 'git
format-patch' and/or 'git send-email' to format & send the mail to the
qemu-devel@nongnu.org mailing list. All patches submitted must contain
a 'Signed-off-by' line from the author. Patches should follow the
guidelines set out in the HACKING and CODING_STYLE files.
Additional information on submitting patches can be found online via
the QEMU website
http://qemu-project.org/Contribute/SubmitAPatch
http://qemu-project.org/Contribute/TrivialPatches
Bug reporting
=============
The QEMU project uses Launchpad as its primary upstream bug tracker. Bugs
found when running code built from QEMU git or upstream released sources
should be reported via:
https://bugs.launchpad.net/qemu/
If using QEMU via an operating system vendor pre-built binary package, it
is preferable to report bugs to the vendor's own bug tracker first. If
the bug is also known to affect latest upstream code, it can also be
reported via launchpad.
For additional information on bug reporting consult:
http://qemu-project.org/Contribute/ReportABug
Contact
=======
The QEMU community can be contacted in a number of ways, with the two
main methods being email and IRC
- qemu-devel@nongnu.org
http://lists.nongnu.org/mailman/listinfo/qemu-devel
- #qemu on irc.oftc.net
Information on additional methods of contacting the community can be
found online via the QEMU website:
http://qemu-project.org/Contribute/StartHere
-- End
46764fe09c