Re: [Qemu-devel] [PATCH] qcow2: Handle EAGAIN returned from update_refcount

[Cole Robinson <crobinso@redhat.com>]

On 06/24/2015 01:05 AM, Jindřich Makovička wrote:
> Fixes a crash during image compression
> 
> Signed-off-by: Jindřich Makovička <makovick@gmail.com>
> ---
>  block/qcow2-refcount.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 

Rich Jones already confirmed that this patch fixes a bug he can reliably
reproduce:

https://bugzilla.redhat.com/show_bug.cgi?id=1214855

- Cole

> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 0632fc3..b0ee42d 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c
> @@ -940,19 +940,21 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size)
>      }
>  
>      free_in_cluster = s->cluster_size - offset_into_cluster(s, offset);
> -    if (!offset || free_in_cluster < size) {
> -        int64_t new_cluster = alloc_clusters_noref(bs, s->cluster_size);
> -        if (new_cluster < 0) {
> -            return new_cluster;
> -        }
> +    do {
> +        if (!offset || free_in_cluster < size) {
> +            int64_t new_cluster = alloc_clusters_noref(bs, s->cluster_size);
> +            if (new_cluster < 0) {
> +                return new_cluster;
> +            }
>  
> -        if (!offset || ROUND_UP(offset, s->cluster_size) != new_cluster) {
> -            offset = new_cluster;
> +            if (!offset || ROUND_UP(offset, s->cluster_size) != new_cluster) {
> +                offset = new_cluster;
> +            }
>          }
> -    }
>  
> -    assert(offset);
> -    ret = update_refcount(bs, offset, size, 1, false, QCOW2_DISCARD_NEVER);
> +        assert(offset);
> +        ret = update_refcount(bs, offset, size, 1, false, QCOW2_DISCARD_NEVER);
> +    } while (ret == -EAGAIN);
>      if (ret < 0) {
>          return ret;
>      }
>