Re: [PATCH 8.0 regression] block/nfs: do not poll within a coroutine

[Peter Maydell]

If you would like this in 8.0 then it needs to be reviewed and in a pullreq
today...

thanks
-- PMM

On Wed, 12 Apr 2023 at 12:27, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> Since the former nfs_get_allocated_file_size is now a coroutine
> function, it must suspend rather than poll.  Switch BDRV_POLL_WHILE()
> to a qemu_coroutine_yield() loop and schedule nfs_co_generic_bh_cb()
> in place of the call to bdrv_wakeup().
>
> Fixes: 82618d7bc341 ("block: Convert bdrv_get_allocated_file_size() to 
> co_wrapper", 2023-02-01)
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block/nfs.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/block/nfs.c b/block/nfs.c
> index 351dc6ec8d14..417defc0cfef 100644
> --- a/block/nfs.c
> +++ b/block/nfs.c
> @@ -726,10 +726,8 @@ nfs_get_allocated_file_size_cb(int ret, struct 
> nfs_context *nfs, void *data,
>      if (task->ret < 0) {
>          error_report("NFS Error: %s", nfs_get_error(nfs));
>      }
> -
> -    /* Set task->complete before reading bs->wakeup.  */
> -    qatomic_mb_set(&task->complete, 1);
> -    bdrv_wakeup(task->bs);
> +    replay_bh_schedule_oneshot_event(task->client->aio_context,
> +                                     nfs_co_generic_bh_cb, task);
>  }
>
>  static int64_t coroutine_fn nfs_co_get_allocated_file_size(BlockDriverState 
> *bs)
> @@ -743,15 +741,19 @@ static int64_t coroutine_fn 
> nfs_co_get_allocated_file_size(BlockDriverState *bs)
>          return client->st_blocks * 512;
>      }
>
> -    task.bs = bs;
> +    nfs_co_init_task(bs, &task);
>      task.st = &st;
> -    if (nfs_fstat_async(client->context, client->fh, 
> nfs_get_allocated_file_size_cb,
> -                        &task) != 0) {
> -        return -ENOMEM;
> -    }
> +    WITH_QEMU_LOCK_GUARD(&client->mutex) {
> +        if (nfs_fstat_async(client->context, client->fh, 
> nfs_get_allocated_file_size_cb,
> +                            &task) != 0) {
> +            return -ENOMEM;
> +        }
>
> -    nfs_set_events(client);
> -    BDRV_POLL_WHILE(bs, !task.complete);
> +       nfs_set_events(client);
> +    }
> +    while (!task.complete) {
> +        qemu_coroutine_yield();
> +    }
>
>      return (task.ret < 0 ? task.ret : st.st_blocks * 512);
>  }