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Re: [Qemu-devel] [Qemu-block] [RFC PATCH 0/7] Fix transactional snapshot
Re: [Qemu-devel] [Qemu-block] [RFC PATCH 0/7] Fix transactional snapshot with virtio-blk dataplane
Thu, 7 May 2015 14:43:43 +0100
On Wed, May 06, 2015 at 07:23:32PM +0800, Fam Zheng wrote:
> Reported by Paolo.
> Unlike the iohandler in main loop, iothreads currently process the event
> notifier used as virtio-blk ioeventfd in all nested aio_poll. This is
> without proper protection, because guest requests could sneak to block layer
> where they mustn't.
> For example, a QMP transaction may involve multiple bdrv_drain_all() in
> handling the list of AioContext it works on. If an aio_poll in one of the
> bdrv_drain_all() happens to process a guest VQ kick by dispatching the
> ioeventfd event, a new guest write is then submitted, and voila, the
> transaction semantics is violated.
> This series avoids this problem by disabling virtio-blk handlers during
> bdrv_drain_all() and transactions.
> If the general approach is right, other transaction types could get the
> blockers similarly, in next revision. And some related bdrv_drain_all() could
> also be changed to bdrv_drain().
> virtio-scsi-dataplane will be a bit more complicated, but still doable. It
> would probably need one more interface abstraction between scsi-disk, scsi-bus
> and virtio-scsi.
> Although other devices don't have a pause/resume callback yet, the
> blk_check_request, which returns -EBUSY if "device io" op blocker is set,
> hopefully cover most cases already.
> Timers and block jobs also generate IO, but it should be fine as long as they
> don't change guest visible data, which is true AFAICT.
> Fam Zheng (7):
> block: Add op blocker type "device IO"
> block: Block "device IO" during bdrv_drain and bdrv_drain_all
> block: Add op blocker notifier list
> block-backend: Add blk_op_blocker_add_notifier
> virtio-blk: Move complete_request to 'ops' structure
> virtio-blk: Don't handle output when there is "device IO" op blocker
> blockdev: Add "device IO" op blocker during snapshot transaction
> block.c | 20 ++++++++++++
> block/block-backend.c | 10 ++++++
> block/io.c | 12 +++++++
> blockdev.c | 7 +++++
> hw/block/dataplane/virtio-blk.c | 36 ++++++++++++++++++---
> hw/block/virtio-blk.c | 69
> include/block/block.h | 9 ++++++
> include/block/block_int.h | 3 ++
> include/hw/virtio/virtio-blk.h | 17 ++++++++--
> include/sysemu/block-backend.h | 2 ++
> 10 files changed, 174 insertions(+), 11 deletions(-)
Please also add a listener to nbd.c so NBD exports cannot submit I/O
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- Re: [Qemu-devel] [RFC PATCH 3/7] block: Add op blocker notifier list, (continued)
- [Qemu-devel] [RFC PATCH 4/7] block-backend: Add blk_op_blocker_add_notifier, Fam Zheng, 2015/05/06
- [Qemu-devel] [RFC PATCH 2/7] block: Block "device IO" during bdrv_drain and bdrv_drain_all, Fam Zheng, 2015/05/06
- [Qemu-devel] [RFC PATCH 5/7] virtio-blk: Move complete_request to 'ops' structure, Fam Zheng, 2015/05/06
- [Qemu-devel] [RFC PATCH 7/7] blockdev: Add "device IO" op blocker during snapshot transaction, Fam Zheng, 2015/05/06
- [Qemu-devel] [RFC PATCH 6/7] virtio-blk: Don't handle output when there is "device IO" op blocker, Fam Zheng, 2015/05/06
- Re: [Qemu-devel] [Qemu-block] [RFC PATCH 0/7] Fix transactional snapshot with virtio-blk dataplane,
Stefan Hajnoczi <=