Re: [BUG qemu 4.0] segfault when unplugging virtio-blk-pci device

[Stefan Hajnoczi]

On Tue, Jan 14, 2020 at 10:50:58AM +0800, Eryu Guan wrote:
> On Mon, Jan 13, 2020 at 04:38:55PM +0000, Stefan Hajnoczi wrote:
> > On Thu, Jan 09, 2020 at 12:58:06PM +0800, Eryu Guan wrote:
> > > On Tue, Jan 07, 2020 at 03:01:01PM +0100, Julia Suvorova wrote:
> > > > On Tue, Jan 7, 2020 at 2:06 PM Eryu Guan <address@hidden> wrote:
> > > > >
> > > > > On Thu, Jan 02, 2020 at 10:08:50AM +0800, Eryu Guan wrote:
> > > > > > On Tue, Dec 31, 2019 at 11:51:35AM +0100, Igor Mammedov wrote:
> > > > > > > On Tue, 31 Dec 2019 18:34:34 +0800
> > > > > > > Eryu Guan <address@hidden> wrote:
> > > > > > >
> > > > > > > > Hi,
> > > > > > > >
> > > > > > > > I'm using qemu 4.0 and hit segfault when tearing down kata 
> > > > > > > > sandbox, I
> > > > > > > > think it's because io completion hits use-after-free when 
> > > > > > > > device is
> > > > > > > > already gone. Is this a known bug that has been fixed? (I went 
> > > > > > > > through
> > > > > > > > the git log but didn't find anything obvious).
> > > > > > > >
> > > > > > > > gdb backtrace is:
> > > > > > > >
> > > > > > > > Core was generated by `/usr/local/libexec/qemu-kvm -name 
> > > > > > > > sandbox-5b8df8c6c6901c3c0a9b02879be10fe8d69d6'.
> > > > > > > > Program terminated with signal 11, Segmentation fault.
> > > > > > > > #0 object_get_class (obj=obj@entry=0x0) at 
> > > > > > > > /usr/src/debug/qemu-4.0/qom/object.c:903
> > > > > > > > 903        return obj->class;
> > > > > > > > (gdb) bt
> > > > > > > > #0  object_get_class (obj=obj@entry=0x0) at 
> > > > > > > > /usr/src/debug/qemu-4.0/qom/object.c:903
> > > > > > > > #1  0x0000558a2c009e9b in virtio_notify_vector 
> > > > > > > > (vdev=0x558a2e7751d0,
> > > > > > > >     vector=<optimized out>) at 
> > > > > > > > /usr/src/debug/qemu-4.0/hw/virtio/virtio.c:1118
> > > > > > > > #2  0x0000558a2bfdcb1e in 
> > > > > > > > virtio_blk_discard_write_zeroes_complete (
> > > > > > > >     opaque=0x558a2f2fd420, ret=0)
> > > > > > > >     at /usr/src/debug/qemu-4.0/hw/block/virtio-blk.c:186
> > > > > > > > #3  0x0000558a2c261c7e in blk_aio_complete (acb=0x558a2eed7420)
> > > > > > > >     at /usr/src/debug/qemu-4.0/block/block-backend.c:1305
> > > > > > > > #4  0x0000558a2c3031db in coroutine_trampoline (i0=<optimized 
> > > > > > > > out>,
> > > > > > > >     i1=<optimized out>) at 
> > > > > > > > /usr/src/debug/qemu-4.0/util/coroutine-ucontext.c:116
> > > > > > > > #5  0x00007f45b2f8b080 in ?? () from /lib64/libc.so.6
> > > > > > > > #6  0x00007fff9ed75780 in ?? ()
> > > > > > > > #7  0x0000000000000000 in ?? ()
> > > > > > > >
> > > > > > > > It seems like qemu was completing a discard/write_zero request, 
> > > > > > > > but
> > > > > > > > parent BusState was already freed & set to NULL.
> > > > > > > >
> > > > > > > > Do we need to drain all pending request before unrealizing 
> > > > > > > > virtio-blk
> > > > > > > > device? Like the following patch proposed?
> > > > > > > >
> > > > > > > > https://lists.gnu.org/archive/html/qemu-devel/2017-06/msg02945.html
> > > > > > > >
> > > > > > > > If more info is needed, please let me know.
> > > > > > >
> > > > > > > may be this will help: 
> > > > > > > https://patchwork.kernel.org/patch/11213047/
> > > > > >
> > > > > > Yeah, this looks promising! I'll try it out (though it's a one-time
> > > > > > crash for me). Thanks!
> > > > >
> > > > > After applying this patch, I don't see the original segfaut and
> > > > > backtrace, but I see this crash
> > > > >
> > > > > [Thread debugging using libthread_db enabled]
> > > > > Using host libthread_db library "/lib64/libthread_db.so.1".
> > > > > Core was generated by `/usr/local/libexec/qemu-kvm -name 
> > > > > sandbox-a2f34a11a7e1449496503bbc4050ae040c0d3'.
> > > > > Program terminated with signal 11, Segmentation fault.
> > > > > #0  0x0000561216a57609 in virtio_pci_notify_write 
> > > > > (opaque=0x5612184747e0, addr=0, val=<optimized out>, size=<optimized 
> > > > > out>) at /usr/src/debug/qemu-4.0/hw/virtio/virtio-pci.c:1324
> > > > > 1324        VirtIOPCIProxy *proxy = 
> > > > > VIRTIO_PCI(DEVICE(vdev)->parent_bus->parent);
> > > > > Missing separate debuginfos, use: debuginfo-install 
> > > > > glib2-2.42.2-5.1.alios7.x86_64 glibc-2.17-260.alios7.x86_64 
> > > > > libgcc-4.8.5-28.alios7.1.x86_64 libseccomp-2.3.1-3.alios7.x86_64 
> > > > > libstdc++-4.8.5-28.alios7.1.x86_64 
> > > > > numactl-libs-2.0.9-5.1.alios7.x86_64 pixman-0.32.6-3.1.alios7.x86_64 
> > > > > zlib-1.2.7-16.2.alios7.x86_64
> > > > > (gdb) bt
> > > > > #0  0x0000561216a57609 in virtio_pci_notify_write 
> > > > > (opaque=0x5612184747e0, addr=0, val=<optimized out>, size=<optimized 
> > > > > out>) at /usr/src/debug/qemu-4.0/hw/virtio/virtio-pci.c:1324
> > > > > #1  0x0000561216835b22 in memory_region_write_accessor (mr=<optimized 
> > > > > out>, addr=<optimized out>, value=<optimized out>, size=<optimized 
> > > > > out>, shift=<optimized out>, mask=<optimized out>, attrs=...) at 
> > > > > /usr/src/debug/qemu-4.0/memory.c:502
> > > > > #2  0x0000561216833c5d in access_with_adjusted_size 
> > > > > (addr=addr@entry=0, value=value@entry=0x7fcdeab1b8a8, 
> > > > > size=size@entry=2, access_size_min=<optimized out>, 
> > > > > access_size_max=<optimized out>, access_fn=0x561216835ac0 
> > > > > <memory_region_write_accessor>, mr=0x56121846d340, attrs=...)
> > > > >     at /usr/src/debug/qemu-4.0/memory.c:568
> > > > > #3  0x0000561216837c66 in memory_region_dispatch_write 
> > > > > (mr=mr@entry=0x56121846d340, addr=0, data=<optimized out>, size=2, 
> > > > > attrs=attrs@entry=...) at /usr/src/debug/qemu-4.0/memory.c:1503
> > > > > #4  0x00005612167e036f in flatview_write_continue 
> > > > > (fv=fv@entry=0x56121852edd0, addr=addr@entry=841813602304, attrs=..., 
> > > > > buf=buf@entry=0x7fce7dd97028 <Address 0x7fce7dd97028 out of bounds>, 
> > > > > len=len@entry=2, addr1=<optimized out>, l=<optimized out>, 
> > > > > mr=0x56121846d340)
> > > > >     at /usr/src/debug/qemu-4.0/exec.c:3279
> > > > > #5  0x00005612167e0506 in flatview_write (fv=0x56121852edd0, 
> > > > > addr=841813602304, attrs=..., buf=0x7fce7dd97028 <Address 
> > > > > 0x7fce7dd97028 out of bounds>, len=2) at 
> > > > > /usr/src/debug/qemu-4.0/exec.c:3318
> > > > > #6  0x00005612167e4a1b in address_space_write (as=<optimized out>, 
> > > > > addr=<optimized out>, attrs=..., buf=<optimized out>, len=<optimized 
> > > > > out>) at /usr/src/debug/qemu-4.0/exec.c:3408
> > > > > #7  0x00005612167e4aa5 in address_space_rw (as=<optimized out>, 
> > > > > addr=<optimized out>, attrs=..., attrs@entry=..., 
> > > > > buf=buf@entry=0x7fce7dd97028 <Address 0x7fce7dd97028 out of bounds>, 
> > > > > len=<optimized out>, is_write=<optimized out>) at 
> > > > > /usr/src/debug/qemu-4.0/exec.c:3419
> > > > > #8  0x0000561216849da1 in kvm_cpu_exec (cpu=cpu@entry=0x56121849aa00) 
> > > > > at /usr/src/debug/qemu-4.0/accel/kvm/kvm-all.c:2034
> > > > > #9  0x000056121682255e in qemu_kvm_cpu_thread_fn 
> > > > > (arg=arg@entry=0x56121849aa00) at /usr/src/debug/qemu-4.0/cpus.c:1281
> > > > > #10 0x0000561216b794d6 in qemu_thread_start (args=<optimized out>) at 
> > > > > /usr/src/debug/qemu-4.0/util/qemu-thread-posix.c:502
> > > > > #11 0x00007fce7bef6e25 in start_thread () from /lib64/libpthread.so.0
> > > > > #12 0x00007fce7bc1ef1d in clone () from /lib64/libc.so.6
> > > > >
> > > > > And I searched and found
> > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1706759 , which has the 
> > > > > same
> > > > > backtrace as above, and it seems commit 7bfde688fb1b ("virtio-blk: Add
> > > > > blk_drain() to virtio_blk_device_unrealize()") is to fix this 
> > > > > particular
> > > > > bug.
> > > > >
> > > > > But I can still hit the bug even after applying the commit. Do I miss
> > > > > anything?
> > > > 
> > > > Hi Eryu,
> > > > This backtrace seems to be caused by this bug (there were two bugs in
> > > > 1706759): https://bugzilla.redhat.com/show_bug.cgi?id=1708480
> > > > Although the solution hasn't been tested on virtio-blk yet, you may
> > > > want to apply this patch:
> > > >     
> > > > https://lists.nongnu.org/archive/html/qemu-devel/2019-12/msg05197.html
> > > > Let me know if this works.
> > > 
> > > Unfortunately, I still see the same segfault & backtrace after applying
> > > commit 421afd2fe8dd ("virtio: reset region cache when on queue
> > > deletion")
> > > 
> > > Anything I can help to debug?
> > 
> > Please post the QEMU command-line and the QMP commands use to remove the
> > device.
> 
> It's a normal kata instance using virtio-fs as rootfs.
> 
> /usr/local/libexec/qemu-kvm -name 
> sandbox-a670786fcb1758d2348eb120939d90ffacf9f049f10b337284ad49bbcd60936d \
>  -uuid e03f6b6b-b80b-40c0-8d5b-0cbfed1305d2 -machine 
> q35,accel=kvm,kernel_irqchip,nvdimm,nosmm,nosmbus,nosata,nopit \
>  -cpu host -qmp 
> unix:/run/vc/vm/a670786fcb1758d2348eb120939d90ffacf9f049f10b337284ad49bbcd60936d/qmp.sock,server,nowait
>  \
>  -qmp 
> unix:/run/vc/vm/debug-a670786fcb1758d2348eb120939d90ffacf9f049f10b337284ad49bbcd60936d/qmp.sock,server,nowait
>  \
>  -m 2048M,slots=10,maxmem=773893M -device 
> pci-bridge,bus=pcie.0,id=pci-bridge-0,chassis_nr=1,shpc=on,addr=2,romfile= \
>  -device virtio-serial-pci,disable-modern=false,id=serial0,romfile= -device 
> virtconsole,chardev=charconsole0,id=console0 \
>  -chardev 
> socket,id=charconsole0,path=/run/vc/vm/a670786fcb1758d2348eb120939d90ffacf9f049f10b337284ad49bbcd60936d/console.sock,server,nowait
>  \
>  -device 
> virtserialport,chardev=metricagent,id=channel10,name=metric.agent.channel.10 \
>  -chardev 
> socket,id=metricagent,path=/run/vc/vm/a670786fcb1758d2348eb120939d90ffacf9f049f10b337284ad49bbcd60936d/metric.agent.channel.sock,server,nowait
>  \
>  -device nvdimm,id=nv0,memdev=mem0 -object 
> memory-backend-file,id=mem0,mem-path=/usr/local/share/containers-image-1.9.0.img,size=268435456
>  \
>  -object rng-random,id=rng0,filename=/dev/urandom -device 
> virtio-rng,rng=rng0,romfile= \
>  -device virtserialport,chardev=charch0,id=channel0,name=agent.channel.0 \
>  -chardev 
> socket,id=charch0,path=/run/vc/vm/a670786fcb1758d2348eb120939d90ffacf9f049f10b337284ad49bbcd60936d/kata.sock,server,nowait
>  \
>  -chardev 
> socket,id=char-6fca044b801a78a1,path=/run/vc/vm/a670786fcb1758d2348eb120939d90ffacf9f049f10b337284ad49bbcd60936d/vhost-fs.sock
>  \
>  -device 
> vhost-user-fs-pci,chardev=char-6fca044b801a78a1,tag=kataShared,cache-size=8192M
>  -netdev tap,id=network-0,vhost=on,vhostfds=3,fds=4 \
>  -device 
> driver=virtio-net-pci,netdev=network-0,mac=76:57:f1:ab:51:5c,disable-modern=false,mq=on,vectors=4,romfile=
>  \
>  -global kvm-pit.lost_tick_policy=discard -vga none -no-user-config 
> -nodefaults -nographic -daemonize \
>  -object memory-backend-file,id=dimm1,size=2048M,mem-path=/dev/shm,share=on 
> -numa node,memdev=dimm1 -kernel /usr/local/share/kernel \
>  -append tsc=reliable no_timer_check rcupdate.rcu_expedited=1 i8042.direct=1 
> i8042.dumbkbd=1 i8042.nopnp=1 i8042.noaux=1 noreplace-smp reboot=k 
> console=hvc0 console=hvc1 iommu=off cryptomgr.notests net.ifnames=0 
> pci=lastbus=0 root=/dev/pmem0p1 rootflags=dax,data=ordered,errors=remount-ro 
> ro rootfstype=ext4 quiet systemd.show_status=false panic=1 nr_cpus=96 
> agent.use_vsock=false init=/usr/lib/systemd/systemd 
> systemd.unit=kata-containers.target systemd.mask=systemd-networkd.service 
> systemd.mask=systemd-networkd.socket \
>  -pidfile 
> /run/vc/vm/a670786fcb1758d2348eb120939d90ffacf9f049f10b337284ad49bbcd60936d/pid
>  \
>  -smp 1,cores=1,threads=1,sockets=96,maxcpus=96
> 
> QMP command to delete device (the device id is just an example, not the
> one caused the crash):
> 
> "{\"arguments\":{\"id\":\"virtio-drive-5967abfb917c8da6\"},\"execute\":\"device_del\"}"
> 
> which has been hot plugged by:
> "{\"arguments\":{\"cache\":{\"direct\":true,\"no-flush\":false},\"driver\":\"raw\",\"file\":{\"driver\":\"file\",\"filename\":\"/dev/dm-18\"},\"node-name\":\"drive-5967abfb917c8da6\"},\"execute\":\"blockdev-add\"}"
> "{\"return\": {}}"
> "{\"arguments\":{\"addr\":\"01\",\"bus\":\"pci-bridge-0\",\"drive\":\"drive-5967abfb917c8da6\",\"driver\":\"virtio-blk-pci\",\"id\":\"virtio-drive-5967abfb917c8da6\",\"romfile\":\"\",\"share-rw\":\"on\"},\"execute\":\"device_add\"}"
> "{\"return\": {}}"

Thanks.  I wasn't able to reproduce this crash with qemu.git/master.

One thing that is strange about the latest backtrace you posted: QEMU is
dispatching the memory access instead of using the ioeventfd code that
that virtio-blk-pci normally takes when a virtqueue is notified.  I
guess this means ioeventfd has already been disabled due to the hot
unplug.

Could you try with machine type "i440fx" instead of "q35"?  I wonder if
pci-bridge/shpc is part of the problem.

Stefan

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