Re: [Qemu-block] [PATCH for-3.1 v2 1/2] block: Don't inactivate children before parents

[Max Reitz]

On 26.11.18 15:16, Kevin Wolf wrote:
> bdrv_child_cb_inactivate() asserts that parents are already inactive
> when children get inactivated. This precondition is necessary because
> parents could still issue requests in their inactivation code.
> 
> When block nodes are created individually with -blockdev, all of them
> are monitor owned and will be returned by bdrv_next() in an undefined
> order (in practice, in the order of their creation, which is usually
> children before parents), which obviously fails the assertion:
> 
> qemu: block.c:899: bdrv_child_cb_inactivate: Assertion `bs->open_flags & 
> BDRV_O_INACTIVE' failed.
> 
> This patch fixes the ordering by skipping nodes with still active
> parents in bdrv_inactivate_recurse() because we know that they will be
> covered by recursion when the last active parent becomes inactive.
> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  block.c | 32 +++++++++++++++++++++++++++++++-
>  1 file changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/block.c b/block.c
> index 5ba3435f8f..e9181c3be7 100644
> --- a/block.c
> +++ b/block.c

[...]

> @@ -4622,6 +4638,14 @@ static int bdrv_inactivate_recurse(BlockDriverState 
> *bs,
>          return -ENOMEDIUM;
>      }
>  
> +    /* Make sure that we don't inactivate a child before its parent.
> +     * It will be covered by recursion from the yet active parent. */
> +    if (bdrv_has_bds_parent(bs, true)) {

Overall the patch looks good to me, apart from the fact that I still
think this should only be checked if setting_flag is true.

(Because BDRV_O_INACTIVE is only set during the second pass, so this
check will lead to the first pass not doing anything (and thus not
calling bs->drv->bdrv_inactivate()) on any non-root bs.)

Max

> +        return 0;
> +    }
> +
> +    assert(!(bs->open_flags & BDRV_O_INACTIVE));
> +
>      if (!setting_flag && bs->drv->bdrv_inactivate) {
>          ret = bs->drv->bdrv_inactivate(bs);
>          if (ret < 0) {

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