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

[Eryu Guan]

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?

Thanks,
Eryu