• Stefan Hajnoczi's avatar
    aio-posix: honor is_external in AioContext polling · 59c9f437
    Stefan Hajnoczi authored
    AioHandlers marked ->is_external must be skipped when aio_node_check()
    fails.  bdrv_drained_begin() needs this to prevent dataplane from
    submitting new I/O requests while another thread accesses the device and
    relies on it being quiesced.
    
    This patch fixes the following segfault:
    
      Program terminated with signal SIGSEGV, Segmentation fault.
      #0  0x00005577f6127dad in bdrv_io_plug (bs=0x5577f7ae52f0) at qemu/block/io.c:2650
      2650            bdrv_io_plug(child->bs);
      [Current thread is 1 (Thread 0x7ff5c4bd1c80 (LWP 10917))]
      (gdb) bt
      #0  0x00005577f6127dad in bdrv_io_plug (bs=0x5577f7ae52f0) at qemu/block/io.c:2650
      #1  0x00005577f6114363 in blk_io_plug (blk=0x5577f7b8ba20) at qemu/block/block-backend.c:1561
      #2  0x00005577f5d4091d in virtio_blk_handle_vq (s=0x5577f9ada030, vq=0x5577f9b3d2a0) at qemu/hw/block/virtio-blk.c:589
      #3  0x00005577f5d4240d in virtio_blk_data_plane_handle_output (vdev=0x5577f9ada030, vq=0x5577f9b3d2a0) at qemu/hw/block/dataplane/virtio-blk.c:158
      #4  0x00005577f5d88acd in virtio_queue_notify_aio_vq (vq=0x5577f9b3d2a0) at qemu/hw/virtio/virtio.c:1304
      #5  0x00005577f5d8aaaf in virtio_queue_host_notifier_aio_poll (opaque=0x5577f9b3d308) at qemu/hw/virtio/virtio.c:2134
      #6  0x00005577f60ca077 in run_poll_handlers_once (ctx=0x5577f79ddbb0) at qemu/aio-posix.c:493
      #7  0x00005577f60ca268 in try_poll_mode (ctx=0x5577f79ddbb0, blocking=true) at qemu/aio-posix.c:569
      #8  0x00005577f60ca331 in aio_poll (ctx=0x5577f79ddbb0, blocking=true) at qemu/aio-posix.c:601
      #9  0x00005577f612722a in bdrv_flush (bs=0x5577f7c20970) at qemu/block/io.c:2403
      #10 0x00005577f60c1b2d in bdrv_close (bs=0x5577f7c20970) at qemu/block.c:2322
      #11 0x00005577f60c20e7 in bdrv_delete (bs=0x5577f7c20970) at qemu/block.c:2465
      #12 0x00005577f60c3ecf in bdrv_unref (bs=0x5577f7c20970) at qemu/block.c:3425
      #13 0x00005577f60bf951 in bdrv_root_unref_child (child=0x5577f7a2de70) at qemu/block.c:1361
      #14 0x00005577f6112162 in blk_remove_bs (blk=0x5577f7b8ba20) at qemu/block/block-backend.c:491
      #15 0x00005577f6111b1b in blk_remove_all_bs () at qemu/block/block-backend.c:245
      #16 0x00005577f60c1db6 in bdrv_close_all () at qemu/block.c:2382
      #17 0x00005577f5e60cca in main (argc=20, argv=0x7ffea6eb8398, envp=0x7ffea6eb8440) at qemu/vl.c:4684
    
    The key thing is that bdrv_close() uses bdrv_drained_begin() and
    virtio_queue_host_notifier_aio_poll() must not be called.
    
    Thanks to Fam Zheng <famz@redhat.com> for identifying the root cause of
    this crash.
    Reported-by: 's avatarAlberto Garcia <berto@igalia.com>
    Signed-off-by: 's avatarStefan Hajnoczi <stefanha@redhat.com>
    Reviewed-by: 's avatarFam Zheng <famz@redhat.com>
    Tested-by: 's avatarAlberto Garcia <berto@igalia.com>
    Message-id: 20170124095350.16679-1-stefanha@redhat.com
    Signed-off-by: 's avatarStefan Hajnoczi <stefanha@redhat.com>
    59c9f437
aio-posix.c 19.9 KB