[PATCH v3 for-5.1 0/2] Fix crash due to NBD export leak

[Vladimir Sementsov-Ogievskiy]

Hi all!

We've faced crash bug, which is reproducing on master branch as well.
The case is described in 01, where fix is suggested.
New iotest in 02 crashes without that fix.

v3: resend for convenience, as all preparatory patches are merged.
01-02: add Eric's r-b and t-b marks

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This is a crash-fix, so it would be good to fix in 5.1. Still neither
Eric nor I are sure in patch 01: is AIO_WAIT_WHILE used correctly?

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Side note: this AIO_WAIT_WHILE may be long, if nbd reconnect is enabled
and connection failed recently. Still it's another story: I think we
actually should disable reconnect in bdrv_close, before drain.

Vladimir Sementsov-Ogievskiy (2):
  nbd: make nbd_export_close_all() synchronous
  iotests: test shutdown when bitmap is exported through NBD

 nbd/server.c               |  8 +++++
 tests/qemu-iotests/299     | 65 ++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/299.out | 10 ++++++
 tests/qemu-iotests/group   |  1 +
 4 files changed, 84 insertions(+)
 create mode 100644 tests/qemu-iotests/299
 create mode 100644 tests/qemu-iotests/299.out

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2.21.0