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

[Max Reitz]

On 26.11.18 12:28, 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.
> 
> 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 | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/block.c b/block.c
> index 5ba3435f8f..0569275e31 100644
> --- a/block.c
> +++ b/block.c
> @@ -4612,6 +4612,22 @@ void bdrv_invalidate_cache_all(Error **errp)
>      }
>  }
>  
> +static bool bdrv_has_active_bds_parent(BlockDriverState *bs)
> +{
> +    BdrvChild *parent;
> +
> +    QLIST_FOREACH(parent, &bs->parents, next_parent) {
> +        if (parent->role->parent_is_bds) {
> +            BlockDriverState *parent_bs = parent->opaque;
> +            if (!(parent_bs->open_flags & BDRV_O_INACTIVE)) {
> +                return true;
> +            }
> +        }
> +    }

Now I see why you say this might make sense as a permission.

> +
> +    return false;
> +}
> +
>  static int bdrv_inactivate_recurse(BlockDriverState *bs,
>                                     bool setting_flag)
>  {
> @@ -4622,6 +4638,12 @@ 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_active_bds_parent(bs)) {
> +        return 0;
> +    }
> +

Hm.  Wouldn't it make more sense to always return early when there are
any BDS parents?  Because if there are any BDS parents and none of them
are active (anymore), then this child will have been inactivated
already, and we can save ourselves the trouble of going through the rest
of the function again.

Do drivers support multiple calls to .bdrv_in_activate() at all?

Max

>      if (!setting_flag && bs->drv->bdrv_inactivate) {
>          ret = bs->drv->bdrv_inactivate(bs);
>          if (ret < 0) {
>

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