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Got a core dump now. The stack trace looks different, but a segfault in malloc should be a sign for heap corruption. And if we overwrite some random memory, we can hit anything. So this could really be the same as in the original description and as in bug 602209.

#0  0x00000037faa75852 in malloc_consolidate () from /lib64/libc.so.6
#1  0x00000037faa786e2 in _int_malloc () from /lib64/libc.so.6
#2  0x00000037faa79f5f in _int_memalign () from /lib64/libc.so.6
#3  0x00000037faa7a5d2 in memalign () from /lib64/libc.so.6
#4  0x00000037faa7a7e9 in posix_memalign () from /lib64/libc.so.6
#5  0x000000000047c837 in qemu_memalign (alignment=<value optimized out>, size=<value optimized out>) at osdep.c:93
#6  0x000000000048bb46 in qcow_aio_setup (bs=0x2272010, sector_num=18082495, qiov=0x7f8fb41f49c0, nb_sectors=48, cb=<value optimized out>, 
    opaque=<value optimized out>, is_write=1) at block/qcow2.c:497
#7  0x000000000048bf30 in qcow_aio_writev (bs=<value optimized out>, sector_num=<value optimized out>, qiov=<value optimized out>, 
    nb_sectors=<value optimized out>, cb=<value optimized out>, opaque=<value optimized out>) at block/qcow2.c:651
#8  0x0000000000477d93 in bdrv_aio_writev (bs=0x2272010, sector_num=18082495, qiov=0x7f8fb41f49c0, nb_sectors=48, cb=<value optimized out>, 
    opaque=<value optimized out>) at block.c:1858
#9  0x0000000000478b5b in bdrv_aio_multiwrite (bs=0x2272010, reqs=0x7f8fbc3605d0, num_reqs=3) at block.c:2049
#10 0x000000000041d3fe in do_multiwrite (bs=<value optimized out>, blkreq=0x7f8fbc3605d0, num_writes=3)
    at /usr/src/debug/qemu-kvm-0.12.1.2/hw/virtio-blk.c:235
#11 0x000000000041daa8 in virtio_blk_handle_output (vdev=0x2305b40, vq=<value optimized out>) at /usr/src/debug/qemu-kvm-0.12.1.2/hw/virtio-blk.c:362
#12 0x000000000042a481 in kvm_handle_io (env=0x22a7900) at /usr/src/debug/qemu-kvm-0.12.1.2/kvm-all.c:538
#13 kvm_run (env=0x22a7900) at /usr/src/debug/qemu-kvm-0.12.1.2/qemu-kvm.c:969
#14 0x000000000042a529 in kvm_cpu_exec (env=<value optimized out>) at /usr/src/debug/qemu-kvm-0.12.1.2/qemu-kvm.c:1652
#15 0x000000000042b14f in kvm_main_loop_cpu (_env=0x22a7900) at /usr/src/debug/qemu-kvm-0.12.1.2/qemu-kvm.c:1894
#16 ap_main_loop (_env=0x22a7900) at /usr/src/debug/qemu-kvm-0.12.1.2/qemu-kvm.c:1944
#17 0x00000037fb207761 in start_thread () from /lib64/libpthread.so.0
#18 0x00000037faae14fd in clone () from /lib64/libc.so.6

The qemu_blockalign parameters look right:

497             acb->buf = acb->orig_buf = qemu_blockalign(bs, qiov->size);
(gdb) p *qiov
$3 = {iov = 0x7f8fb41f09b8, niov = 2, nalloc = -1, size = 24576}
(gdb) p *bs
$4 = {total_sectors = 41943040, read_only = 0, keep_read_only = 0, open_flags = 34, removable = 0, locked = 0, encrypted = 0, valid_key = 0, sg = 0, 
  change_cb = 0, change_opaque = 0x0, drv = 0x859c00, opaque = 0x2272920, filename = "/dev/vgtest/lvtest", '\000' <repeats 1005 times>, 
  backing_file = '\000' <repeats 1023 times>, backing_format = '\000' <repeats 15 times>, is_temporary = 0, media_changed = 1, backing_hd = 0x0, 
  file = 0x2272ca0, sync_aiocb = 0x0, rd_bytes = 2284544, wr_bytes = 878585856, rd_ops = 550, wr_ops = 1652, wr_highest_sector = 41943039, 
  growable = 0, buffer_alignment = 512, enable_write_cache = 1, cyls = 16383, heads = 16, secs = 63, translation = 2, type = 0, 
  device_name = "drive-virtio-disk0", '\000' <repeats 13 times>, dirty_bitmap = 0x0, list = {tqe_next = 0x0, tqe_prev = 0x857f20}, private = 0x0}

ok .then follow it in bug 602209/

*** This bug has been marked as a duplicate of bug 602209 ***