On Mon, 7 Dec 2015 11:02:51 +0100
Cornelia Huck <cornelia.h...@de.ibm.com> wrote:
> On Thu, 3 Dec 2015 13:00:00 +0800
> Stefan Hajnoczi <stefa...@redhat.com> wrote:
>
> > From: Fam Zheng <f...@redhat.com>
> >
> > The assertion problem was noticed in 06c3916b35a, but it wasn't
> > completely fixed, because even though the req is not marked as
> > serialising, it still gets serialised by wait_serialising_requests
> > against other serialising requests, which could lead to the same
> > assertion failure.
> >
> > Fix it by even more explicitly skipping the serialising for this
> > specific case.
> >
> > Signed-off-by: Fam Zheng <f...@redhat.com>
> > Message-id: 1448962590-2842-2-git-send-email-f...@redhat.com
> > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> > ---
> > block/backup.c | 2 +-
> > block/io.c | 12 +++++++-----
> > include/block/block.h | 4 ++--
> > trace-events | 2 +-
> > 4 files changed, 11 insertions(+), 9 deletions(-)
>
> This one causes segfaults for me:
>
> Program received signal SIGSEGV, Segmentation fault.
> bdrv_is_inserted (bs=0x800000000000) at /data/git/yyy/qemu/block.c:3071
> 3071 if (!drv) {
>
> (gdb) bt
> #0 bdrv_is_inserted (bs=0x800000000000) at /data/git/yyy/qemu/block.c:3071
> #1 0x0000000080216974 in blk_is_inserted (blk=<optimized out>)
> at /data/git/yyy/qemu/block/block-backend.c:986
> #2 0x00000000802169c6 in blk_is_available (blk=blk@entry=0x3ffb17e7960)
> at /data/git/yyy/qemu/block/block-backend.c:991
> #3 0x0000000080216d12 in blk_check_byte_request
> (blk=blk@entry=0x3ffb17e7960,
> offset=offset@entry=4928966656, size=16384)
> at /data/git/yyy/qemu/block/block-backend.c:558
> #4 0x0000000080216df2 in blk_check_request (blk=blk@entry=0x3ffb17e7960,
> sector_num=sector_num@entry=9626888, nb_sectors=nb_sectors@entry=32)
> at /data/git/yyy/qemu/block/block-backend.c:589
> #5 0x0000000080217ee8 in blk_aio_readv (blk=0x3ffb17e7960, sector_num=
> 9626888, iov=0x8098c658, nb_sectors=<optimized out>, cb=
> 0x80081150 <virtio_blk_rw_complete>, opaque=0x80980620)
> at /data/git/yyy/qemu/block/block-backend.c:727
> #6 0x000000008008186e in submit_requests (niov=<optimized out>,
> num_reqs=<optimized out>, start=<optimized out>, mrb=<optimized out>,
> blk=<optimized out>) at /data/git/yyy/qemu/hw/block/virtio-blk.c:366
> #7 virtio_blk_submit_multireq (mrb=<optimized out>, blk=<optimized out>)
> at /data/git/yyy/qemu/hw/block/virtio-blk.c:444
> #8 virtio_blk_submit_multireq (blk=0x3ffb17e7960, mrb=0x3ffffffeb58)
> at /data/git/yyy/qemu/hw/block/virtio-blk.c:389
> #9 0x00000000800823ee in virtio_blk_handle_output (vdev=<optimized out>,
> vq=<optimized out>) at /data/git/yyy/qemu/hw/block/virtio-blk.c:615
> #10 0x00000000801e367e in aio_dispatch (ctx=0x80918520)
> at /data/git/yyy/qemu/aio-posix.c:326
> #11 0x00000000801d28b0 in aio_ctx_dispatch (source=<optimized out>,
> callback=<optimized out>, user_data=<optimized out>)
> at /data/git/yyy/qemu/async.c:231
> #12 0x000003fffd36a05a in g_main_context_dispatch ()
> from /lib64/libglib-2.0.so.0
> #13 0x00000000801e0ffa in glib_pollfds_poll ()
> at /data/git/yyy/qemu/main-loop.c:211
> #14 os_host_main_loop_wait (timeout=<optimized out>)
> at /data/git/yyy/qemu/main-loop.c:256
> #15 main_loop_wait (nonblocking=<optimized out>)
> at /data/git/yyy/qemu/main-loop.c:504
> #16 0x00000000800148a6 in main_loop () at /data/git/yyy/qemu/vl.c:1923
> #17 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>)
> at /data/git/yyy/qemu/vl.c:4684
>
> Relevant part of command line:
>
> -drive
> file=/dev/sda,if=none,id=drive-virtio-disk0,format=raw,serial=ccwzfcp1,cache=none
> -device
> virtio-blk-ccw,devno=fe.0.0001,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1,scsi=off
I played around a bit. The main part of this change seems to be calling
wait_serialising_requests() conditionally; reverting this makes the
guest boot again.
I then tried to find out when wait_serialising_requests() was NOT
called and added fprintfs: well, it was _always_ called. I then added a
fprintf for flags at the beginning of the function: this produced a
segfault no matter whether wait_serialising_requests() was called
conditionally or unconditionally. Weird race?
Anything further I can do? I guess this patch fixes a bug for someone,
but it means insta-death for my setup...
