Re: [RFC PATCH] block/io.c: Flush parent for quorum in generic code

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Wed, May 12, 2021 at 03:49:57PM +0800, Zhang Chen wrote:
> Fix the issue from this patch:
> [PATCH] block: Flush all children in generic code
> From 883833e29cb800b4d92b5d4736252f4004885191
> 
> Quorum driver do not have the primary child.
> It will caused guest block flush issue when use quorum and NBD.
> The vm guest flushes failed，and then guest filesystem is shutdown.
> 
> Signed-off-by: Zhang Chen <chen.zhang@intel.com>
> Reported-by: Minghao Yuan <meeho@qq.com>
> ---
>  block/io.c | 31 ++++++++++++++++++++++---------
>  1 file changed, 22 insertions(+), 9 deletions(-)
...
> +flush_data:
> +    if (no_primary_child) {
> +        /* Flush parent */
> +        ret = bs->file ? bdrv_co_flush(bs->file->bs) : 0;
> +    } else {
> +        /* Flush childrens */
> +        ret = 0;
> +        QLIST_FOREACH(child, &bs->children, next) {
> +            if (child->perm & (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED)) {
> +                int this_child_ret = bdrv_co_flush(child->bs);
> +                if (!ret) {
> +                    ret = this_child_ret;
> +                }
>              }
>          }

I'm missing something:

The quorum driver has a valid bs->children list even though it does not
have a primary child. Why does QLIST_FOREACH() loop fail for you?

Does this patch effectively skip bdrv_co_flush() calls on all quorum
children? That seems wrong since children need to be flushed so that
data is persisted.

Stefan

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