v2:
* Use StrOrNull for x-blockdev-set-iothread iothread argument [eblake]
(This is for QEMU 2.12 because this bug is not -rc4 critical)
Previously AioContext was held across QMP 'transaction' in an attempt to
achieve bdrv_drained_begin/end() semantics. Nowadays we have
bdrv_drained_begin/end() and the AioContext lock just protects state.
Therefore there is no reason to hold AioContext across
.prepare/.commit/.abort/.clean() anymore.
Besides being cleanup-worthy, holding AioContext also exposes a bug:
BDRV_POLL_WHILE() doesn't support recursive AioContext locking and will hang if
depth > 1. This is easy to trigger by submitting a transaction with 2 actions
that touch two drives assigned to an IOThread. The IOThread's AioContext will
be locked twice and BDRV_POLL_WHILE() will hang.
BDRV_POLL_WHILE() is best fixed by eliminating the AioContext lock entirely in
favor of fine-grained locking. I discussed some fixes for BDRV_POLL_WHILE()
with Paolo but we came to the conclusion that it will just add complexity when
we really want to stop using AioContext locking.
Summary:
* Patch 1 fixes missing AioContext lock protection
* Patches 2-6 clean up excessive AioContext locked regions in QMP
'transaction' to solve the hang
* Patches 7-9 add a qemu-iotests test case and the necessary infrastructure
Stefan Hajnoczi (9):
blockdev: hold AioContext for bdrv_unref() in
external_snapshot_clean()
block: don't keep AioContext acquired after
external_snapshot_prepare()
block: don't keep AioContext acquired after drive_backup_prepare()
block: don't keep AioContext acquired after blockdev_backup_prepare()
block: don't keep AioContext acquired after
internal_snapshot_prepare()
block: drop unused BlockDirtyBitmapState->aio_context field
iothread: add iothread_by_id() API
blockdev: add x-blockdev-set-iothread testing command
qemu-iotests: add 202 external snapshots IOThread test
qapi/block-core.json | 36 +++++++
include/sysemu/iothread.h | 1 +
blockdev.c | 258 +++++++++++++++++++++++++++++++++------------
iothread.c | 7 ++
tests/qemu-iotests/202 | 95 +++++++++++++++++
tests/qemu-iotests/202.out | 11 ++
tests/qemu-iotests/group | 1 +
7 files changed, 339 insertions(+), 70 deletions(-)
create mode 100755 tests/qemu-iotests/202
create mode 100644 tests/qemu-iotests/202.out
--
2.14.3
