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

[Eryu Guan]

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!

Eryu