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

[Igor Mammedov]

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/


> 
> Thanks,
> Eryu
>