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Re: [Qemu-block] [PATCH v3 28/44] block: Fix pending requests check in b


From: Alberto Garcia
Subject: Re: [Qemu-block] [PATCH v3 28/44] block: Fix pending requests check in bdrv_append()
Date: Wed, 04 Oct 2017 12:24:05 +0200
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Tue 28 Feb 2017 01:54:13 PM CET, Kevin Wolf wrote:
> bdrv_append() cares about isolation of the node that it modifies, but
> not about activity in some subtree below it. Instead of using the
> recursive bdrv_requests_pending(), directly check bs->in_flight, which
> considers only the node in question.
>
> Signed-off-by: Kevin Wolf <address@hidden>
> Reviewed-by: Max Reitz <address@hidden>
> ---
>  block.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/block.c b/block.c
> index 9e538a5..5189c7c 100644
> --- a/block.c
> +++ b/block.c
> @@ -2897,8 +2897,8 @@ static void change_parent_backing_link(BlockDriverState 
> *from,
>   */
>  void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top)
>  {
> -    assert(!bdrv_requests_pending(bs_top));
> -    assert(!bdrv_requests_pending(bs_new));
> +    assert(!atomic_read(&bs_top->in_flight));
> +    assert(!atomic_read(&bs_new->in_flight));
>  
>      bdrv_ref(bs_top);

I don't know if there's still any maintenance on the v2.8.x branch, but
I can make v2.8.1.1 crash easily because of this failing assertion.
Applying this patch fixes the issue.

I can provide more details if needed.

Regards,

Berto



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