Re: [Qemu-devel] [PATCH for-2.11 4/4] block: Expect graph changes in bdrv_parent_drained_begin/end

[Jeff Cody <jcody@redhat.com>]

On Tue, Nov 28, 2017 at 04:43:50PM +0100, Kevin Wolf wrote:
> The .drained_begin/end callbacks can (directly or indirectly via
> aio_poll()) cause block nodes to be removed or the current BdrvChild to
> point to a different child node.
> 
> Use QLIST_FOREACH_SAFE() to make sure we don't access invalid
> BlockDriverStates or accidentally continue iterating the parents of the
> new child node instead of the node we actually came from.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/io.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/block/io.c b/block/io.c
> index 4fdf93a014..6773926fc1 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -42,9 +42,9 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
>  
>  void bdrv_parent_drained_begin(BlockDriverState *bs)
>  {
> -    BdrvChild *c;
> +    BdrvChild *c, *next;
>  
> -    QLIST_FOREACH(c, &bs->parents, next_parent) {
> +    QLIST_FOREACH_SAFE(c, &bs->parents, next_parent, next) {
>          if (c->role->drained_begin) {
>              c->role->drained_begin(c);
>          }
> @@ -53,9 +53,9 @@ void bdrv_parent_drained_begin(BlockDriverState *bs)
>  
>  void bdrv_parent_drained_end(BlockDriverState *bs)
>  {
> -    BdrvChild *c;
> +    BdrvChild *c, *next;
>  
> -    QLIST_FOREACH(c, &bs->parents, next_parent) {
> +    QLIST_FOREACH_SAFE(c, &bs->parents, next_parent, next) {
>          if (c->role->drained_end) {
>              c->role->drained_end(c);
>          }
> -- 
> 2.13.6
> 
Reviewed-by: Jeff Cody <jcody@redhat.com>