Re: [Qemu-block] [PATCH v2 3/3] block-backend: Queue requests while drained

[Max Reitz]

On 07.08.19 16:46, Kevin Wolf wrote:
> This fixes devices like IDE that can still start new requests from I/O
> handlers in the CPU thread while the block backend is drained.
> 
> The basic assumption is that in a drain section, no new requests should
> be allowed through a BlockBackend (blk_drained_begin/end don't exist,
> we get drain sections only on the node level). However, there are two
> special cases where requests should not be queued:
> 
> 1. Block jobs: We already make sure that block jobs are paused in a
>    drain section, so they won't start new requests. However, if the
>    drain_begin is called on the job's BlockBackend first, it can happen
>    that we deadlock because the job stays busy until it reaches a pause
>    point - which it can't if its requests aren't processed any more.
> 
>    The proper solution here would be to make all requests through the
>    job's filter node instead of using a BlockBackend. For now, just
>    disabling request queuing on the job BlockBackend is simpler.
> 
> 2. In test cases where making requests through bdrv_* would be
>    cumbersome because we'd need a BdrvChild. As we already got the
>    functionality to disable request queuing from 1., use it in tests,
>    too, for convenience.
> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  include/sysemu/block-backend.h |  1 +
>  block/backup.c                 |  1 +
>  block/block-backend.c          | 53 ++++++++++++++++++++++++++++++++--
>  block/commit.c                 |  2 ++
>  block/mirror.c                 |  1 +
>  blockjob.c                     |  3 ++
>  tests/test-bdrv-drain.c        |  1 +
>  7 files changed, 59 insertions(+), 3 deletions(-)

Reviewed-by: Max Reitz <address@hidden>

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