Re: [Qemu-devel] [PATCH] blockdev: fix missed target unref for drive-backup

[Kevin Wolf <kwolf@redhat.com>]

Am 10.05.2019 um 23:52 hat John Snow geschrieben:
> If the bitmap can't be used for whatever reason, we skip putting down
> the reference. Fix that.
> 
> In practice, this means that if you attempt to gracefully exit QEMU
> after a backup command being rejected, bdrv_close_all will fail and
> tell you some unpleasant things via assert().
> 
> Reported-by: aihua liang <aliang@redhat.com>
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1703916
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  blockdev.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 79fbac8450..278ecdd122 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -3525,8 +3525,7 @@ static BlockJob *do_drive_backup(DriveBackup *backup, JobTxn *txn,
>      if (set_backing_hd) {
>          bdrv_set_backing_hd(target_bs, source, &local_err);
>          if (local_err) {
> -            bdrv_unref(target_bs);
> -            goto out;
> +            goto unref;
>          }
>      }
>  
> @@ -3534,11 +3533,10 @@ static BlockJob *do_drive_backup(DriveBackup *backup, JobTxn *txn,
>          bmap = bdrv_find_dirty_bitmap(bs, backup->bitmap);
>          if (!bmap) {
>              error_setg(errp, "Bitmap '%s' could not be found", backup->bitmap);
> -            bdrv_unref(target_bs);
> -            goto out;
> +            goto unref;
>          }
>          if (bdrv_dirty_bitmap_check(bmap, BDRV_BITMAP_DEFAULT, errp)) {
> -            goto out;
> +            goto unref;
>          }
>      }
>      if (!backup->auto_finalize) {
> @@ -3552,12 +3550,12 @@ static BlockJob *do_drive_backup(DriveBackup *backup, JobTxn *txn,
>                              backup->sync, bmap, backup->compress,
>                              backup->on_source_error, backup->on_target_error,
>                              job_flags, NULL, NULL, txn, &local_err);
> -    bdrv_unref(target_bs);
>      if (local_err != NULL) {
>          error_propagate(errp, local_err);
> -        goto out;

Please leave a 'goto unref' here so we can later add more code without
modifying unrelated error paths (or, more likely, forgetting to modify
them).

>      }
>  
> +unref:
> +    bdrv_unref(target_bs);
>  out:
>      aio_context_release(aio_context);
>      return job;

With this fixed:
Reviewed-by: Kevin Wolf <kwolf@redhat.com>