Comment 0 for bug 1805256

On the HiSilicon D06 system - a 96 core NUMA arm64 box - qemu-img frequently hangs (~50% of the time) with this command:

qemu-img convert -f qcow2 -O qcow2 /tmp/cloudimg /tmp/cloudimg2

Where "cloudimg" is a standard qcow2 Ubuntu cloud image. This qcow2->qcow2 conversion happens to be something uvtool does every time it fetches images.

Once hung, attaching gdb gives the following backtrace:

(gdb) bt
#0 0x0000ffffae4f8154 in __GI_ppoll (fds=0xaaaae8a67dc0, nfds=187650274213760,
    timeout=<optimized out>, timeout@entry=0x0, sigmask=0xffffc123b950)
    at ../sysdeps/unix/sysv/linux/ppoll.c:39
#1 0x0000aaaabbefaf00 in ppoll (__ss=0x0, __timeout=0x0, __nfds=<optimized out>,
    __fds=<optimized out>) at /usr/include/aarch64-linux-gnu/bits/poll2.h:77
#2 qemu_poll_ns (fds=<optimized out>, nfds=<optimized out>,
    timeout=timeout@entry=-1) at util/qemu-timer.c:322
#3 0x0000aaaabbefbf80 in os_host_main_loop_wait (timeout=-1)
    at util/main-loop.c:233
#4 main_loop_wait (nonblocking=<optimized out>) at util/main-loop.c:497
#5 0x0000aaaabbe2aa30 in convert_do_copy (s=0xffffc123bb58) at qemu-img.c:1980
#6 img_convert (argc=<optimized out>, argv=<optimized out>) at qemu-img.c:2456
#7 0x0000aaaabbe2333c in main (argc=7, argv=<optimized out>) at qemu-img.c:4975

Reproduced w/ latest QEMU git (@ 53744e0a182)