Re: [qemu-s390x] [Qemu-devel] [BUG] I/O thread segfault for QEMU on s390x

[Stefan Hajnoczi]

On Fri, Mar 02, 2018 at 10:30:57AM -0500, Farhan Ali wrote:
> 
> 
> On 03/02/2018 04:23 AM, Stefan Hajnoczi wrote:
> > On Thu, Mar 01, 2018 at 09:33:35AM -0500, Farhan Ali wrote:
> > > Hi,
> > > 
> > > I have been noticing some segfaults for QEMU on s390x, and I have been
> > > hitting this issue quite reliably (at least once in 10 runs of a test 
> > > case).
> > > The qemu version is 2.11.50, and I have systemd created coredumps
> > > when this happens.
> > > 
> > > Here is a back trace of the segfaulting thread:
> > The backtrace looks normal.
> > 
> > Please post the QEMU command-line and the details of the segfault (which
> > memory access faulted?).
> > 
> 
> 
> I was able to create another crash today and here is the qemu comand line
> 
> /usr/bin/qemu-kvm -name guest=sles,debug-threads=on \
> -S -object 
> secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-2-sles/master-key.aes
> \
> -machine s390-ccw-virtio-2.12,accel=kvm,usb=off,dump-guest-core=off \
> -m 4096 -realtime mlock=off -smp 8,sockets=8,cores=1,threads=1 \
> -object iothread,id=iothread1 -object iothread,id=iothread2 -uuid
> b83a596b-3a1a-4ac9-9f3e-d9a4032ee52c \
> -display none -no-user-config -nodefaults -chardev 
> socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-2-sles/monitor.sock,server,nowait
> 
> -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown
> \
> -boot strict=on -drive 
> file=/dev/mapper/360050763998b0883980000002400002b,format=raw,if=none,id=drive-virtio-disk0,cache=none,aio=native
> -device 
> virtio-blk-ccw,iothread=iothread1,scsi=off,devno=fe.0.0001,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
> -drive 
> file=/dev/mapper/360050763998b0883980000002800002f,format=raw,if=none,id=drive-virtio-disk1,cache=none,aio=native
> -device 
> virtio-blk-ccw,iothread=iothread2,scsi=off,devno=fe.0.0002,drive=drive-virtio-disk1,id=virtio-disk1
> -netdev tap,fd=24,id=hostnet0,vhost=on,vhostfd=26 -device
> virtio-net-ccw,netdev=hostnet0,id=net0,mac=02:38:a6:36:e8:1f,devno=fe.0.0000
> -chardev pty,id=charconsole0 -device
> sclpconsole,chardev=charconsole0,id=console0 -device
> virtio-balloon-ccw,id=balloon0,devno=fe.3.ffba -msg timestamp=on
> 
> 
> This the latest back trace on the segfaulting thread, and it seems to
> segfault in swapcontext.
> 
> Program terminated with signal SIGSEGV, Segmentation fault.
> #0  0x000003ff8595202c in swapcontext () from /lib64/libc.so.6

Please include the following gdb output:

  (gdb) disas swapcontext
  (gdb) i r

That way it's possible to see which instruction faulted and which
registers were being accessed.

> This is the remaining back trace:
> 
> #0  0x000003ff8595202c in swapcontext () from /lib64/libc.so.6
> #1  0x000002aa33b45566 in qemu_coroutine_new () at
> util/coroutine-ucontext.c:164
> #2  0x000002aa33b43eac in qemu_coroutine_create
> (address@hidden <blk_aio_write_entry>,
> address@hidden) at util/qemu-coroutine.c:76
> #3  0x000002aa33a954da in blk_aio_prwv (blk=0x2aa4f0efda0, offset=<optimized
> out>, bytes=<optimized out>, qiov=0x3ff74019080,
> address@hidden <blk_aio_write_entry>, flags=0,
>     cb=0x2aa338c62e8 <virtio_blk_rw_complete>, opaque=0x3ff74019020) at
> block/block-backend.c:1299
> #4  0x000002aa33a9563e in blk_aio_pwritev (blk=<optimized out>,
> offset=<optimized out>, qiov=<optimized out>, flags=<optimized out>,
> cb=<optimized out>, opaque=0x3ff74019020) at block/block-backend.c:1400
> #5  0x000002aa338c6a38 in submit_requests (niov=<optimized out>, num_reqs=1,
> start=<optimized out>, mrb=0x3ff831fe6e0, blk=<optimized out>) at
> /usr/src/debug/qemu-2.11.50/hw/block/virtio-blk.c:369
> #6  virtio_blk_submit_multireq (blk=<optimized out>,
> address@hidden) at
> /usr/src/debug/qemu-2.11.50/hw/block/virtio-blk.c:426
> #7  0x000002aa338c7b78 in virtio_blk_handle_vq (s=0x2aa4f2507c8,
> vq=0x3ff869df010) at /usr/src/debug/qemu-2.11.50/hw/block/virtio-blk.c:620
> #8  0x000002aa338ebdf2 in virtio_queue_notify_aio_vq (vq=0x3ff869df010) at
> /usr/src/debug/qemu-2.11.50/hw/virtio/virtio.c:1515
> #9  0x000002aa33b2df46 in aio_dispatch_handlers
> (address@hidden) at util/aio-posix.c:406
> #10 0x000002aa33b2eb50 in aio_poll (ctx=0x2aa4f0ca050,
> address@hidden) at util/aio-posix.c:692
> #11 0x000002aa33957f6a in iothread_run (opaque=0x2aa4f0c9630) at
> iothread.c:60
> #12 0x000003ff86987e82 in start_thread () from /lib64/libpthread.so.0
> #13 0x000003ff85a11596 in thread_start () from /lib64/libc.so.6
> Backtrace stopped: previous frame identical to this frame (corrupt stack?)
>

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