debian/patches/extra/0006-aio-add-missing-aio_notify-to-aio_enable_external.patch

   1 From c9d7fd0fd5736afd1f6c508f2b5f1ae0608847bd Mon Sep 17 00:00:00 2001
   2 From: Stefan Hajnoczi <stefanha@redhat.com>
   3 Date: Mon, 8 May 2017 14:07:05 -0400
   4 Subject: [PATCH 06/15] aio: add missing aio_notify() to aio_enable_external()
   5
   6 The main loop uses aio_disable_external()/aio_enable_external() to
   7 temporarily disable processing of external AioContext clients like
   8 device emulation.
   9
  10 This allows monitor commands to quiesce I/O and prevent the guest from
  11 submitting new requests while a monitor command is in progress.
  12
  13 The aio_enable_external() API is currently broken when an IOThread is in
  14 aio_poll() waiting for fd activity when the main loop re-enables
  15 external clients.  Incrementing ctx->external_disable_cnt does not wake
  16 the IOThread from ppoll(2) so fd processing remains suspended and leads
  17 to unresponsive emulated devices.
  18
  19 This patch adds an aio_notify() call to aio_enable_external() so the
  20 IOThread is kicked out of ppoll(2) and will re-arm the file descriptors.
  21
  22 The bug can be reproduced as follows:
  23
  24   $ qemu -M accel=kvm -m 1024 \
  25          -object iothread,id=iothread0 \
  26          -device virtio-scsi-pci,iothread=iothread0,id=virtio-scsi-pci0 \
  27          -drive if=none,id=drive0,aio=native,cache=none,format=raw,file=test.img \
  28          -device scsi-hd,id=scsi-hd0,drive=drive0 \
  29          -qmp tcp::5555,server,nowait
  30
  31   $ scripts/qmp/qmp-shell localhost:5555
  32   (qemu) blockdev-snapshot-sync device=drive0 snapshot-file=sn1.qcow2
  33          mode=absolute-paths format=qcow2
  34
  35 After blockdev-snapshot-sync completes the SCSI disk will be
  36 unresponsive.  This leads to request timeouts inside the guest.
  37
  38 Reported-by: Qianqian Zhu <qizhu@redhat.com>
  39 Reviewed-by: Fam Zheng <famz@redhat.com>
  40 Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
  41 Message-id: 20170508180705.20609-1-stefanha@redhat.com
  42 Suggested-by: Fam Zheng <famz@redhat.com>
  43 Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
  44 ---
  45  include/block/aio.h | 10 ++++++++--
  46  1 file changed, 8 insertions(+), 2 deletions(-)
  47
  48 diff --git a/include/block/aio.h b/include/block/aio.h
  49 index 406e32305a..e9aeeaec94 100644
  50 --- a/include/block/aio.h
  51 +++ b/include/block/aio.h
  52 @@ -454,8 +454,14 @@ static inline void aio_disable_external(AioContext *ctx)
  53   */
  54  static inline void aio_enable_external(AioContext *ctx)
  55  {
  56 -    assert(ctx->external_disable_cnt > 0);
  57 -    atomic_dec(&ctx->external_disable_cnt);
  58 +    int old;
  59 +
  60 +    old = atomic_fetch_dec(&ctx->external_disable_cnt);
  61 +    assert(old > 0);
  62 +    if (old == 1) {
  63 +        /* Kick event loop so it re-arms file descriptors */
  64 +        aio_notify(ctx);
  65 +    }
  66  }
  67
  68  /**
  69 --
  70 2.11.0
  71