On 08/03/2016 11:11, Stefan Hajnoczi wrote:
> This reverts commit df9a681dc9ad41c9cdeb9ecc5d060ba9abd27e01.
>
> Note that commit df9a681dc9ad41c9cdeb9ecc5d060ba9abd27e01 included some
> unrelated hunks, possibly due to a merge failure or an overlooked
> squash. This only reverts the qed .bdrv_drain() implementation.
>
> The qed .bdrv_drain() implementation is unsafe and can lead to a double
> request completion.
>
> Paolo Bonzini reports:
> "The problem is that bdrv_qed_drain calls qed_plug_allocating_write_reqs
> unconditionally, but this is not correct if an allocating write is
> queued. In this case, qed_unplug_allocating_write_reqs will restart the
> allocating write and possibly cause it to complete. The aiocb however
> is still in use for the L2/L1 table writes, and will then be completed
> again as soon as the table writes are stable."
>
> For QEMU 2.6 we can simply revert this commit. A full solution for the
> qed need check timer may be added if the bdrv_drain() implementation is
> extended.
>
> Reported-by: Paolo Bonzini <pbonz...@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
Acked-by: Paolo Bonzini <pbonz...@redhat.com>
Paolo
> ---
> block/qed.c | 13 -------------
> 1 file changed, 13 deletions(-)
>
> Passes ./check -qed.
>
> diff --git a/block/qed.c b/block/qed.c
> index 404be1e..3da8021 100644
> --- a/block/qed.c
> +++ b/block/qed.c
> @@ -376,18 +376,6 @@ static void bdrv_qed_attach_aio_context(BlockDriverState
> *bs,
> }
> }
>
> -static void bdrv_qed_drain(BlockDriverState *bs)
> -{
> - BDRVQEDState *s = bs->opaque;
> -
> - /* Cancel timer and start doing I/O that were meant to happen as if it
> - * fired, that way we get bdrv_drain() taking care of the ongoing
> requests
> - * correctly. */
> - qed_cancel_need_check_timer(s);
> - qed_plug_allocating_write_reqs(s);
> - bdrv_aio_flush(s->bs, qed_clear_need_check, s);
> -}
> -
> static int bdrv_qed_open(BlockDriverState *bs, QDict *options, int flags,
> Error **errp)
> {
> @@ -1692,7 +1680,6 @@ static BlockDriver bdrv_qed = {
> .bdrv_check = bdrv_qed_check,
> .bdrv_detach_aio_context = bdrv_qed_detach_aio_context,
> .bdrv_attach_aio_context = bdrv_qed_attach_aio_context,
> - .bdrv_drain = bdrv_qed_drain,
> };
>
> static void bdrv_qed_init(void)
>
