Re: [Qemu-devel] [PATCH 19/19] block: Keep nodes drained between reopen_queue/multiple

[Fam Zheng <famz@redhat.com>]

On Wed, 12/20 11:34, Kevin Wolf wrote:
> The bdrv_reopen*() implementation doesn't like it if the graph is
> changed between queuing nodes for reopen and actually reopening them
> (one of the reasons is that queuing can be recursive).
> 
> So instead of draining the device only in bdrv_reopen_multiple(),
> require that callers already drained all affected nodes, and assert this
> in bdrv_reopen_queue().
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block.c             | 23 ++++++++++++++++-------
>  block/replication.c |  6 ++++++
>  qemu-io-cmds.c      |  3 +++
>  3 files changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 37f8639fe9..cfd39bea10 100644
> --- a/block.c
> +++ b/block.c
> @@ -2774,6 +2774,7 @@ BlockDriverState *bdrv_open(const char *filename, const char *reference,
>   * returns a pointer to bs_queue, which is either the newly allocated
>   * bs_queue, or the existing bs_queue being used.
>   *
> + * bs must be drained between bdrv_reopen_queue() and bdrv_reopen_multiple().
>   */
>  static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
>                                                   BlockDriverState *bs,
> @@ -2789,6 +2790,11 @@ static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
>      BdrvChild *child;
>      QDict *old_options, *explicit_options;
>  
> +    /* Make sure that the caller remembered to use a drained section. This is
> +     * important to avoid graph changes between the recursive queuing here and
> +     * bdrv_reopen_multiple(). */
> +    assert(bs->quiesce_counter > 0);
> +
>      if (bs_queue == NULL) {
>          bs_queue = g_new0(BlockReopenQueue, 1);
>          QSIMPLEQ_INIT(bs_queue);
> @@ -2913,6 +2919,8 @@ BlockReopenQueue *bdrv_reopen_queue(BlockReopenQueue *bs_queue,
>   * If all devices prepare successfully, then the changes are committed
>   * to all devices.
>   *
> + * All affected nodes must be drained between bdrv_reopen_queue() and
> + * bdrv_reopen_multiple().
>   */
>  int bdrv_reopen_multiple(AioContext *ctx, BlockReopenQueue *bs_queue, Error **errp)
>  {
> @@ -2922,11 +2930,8 @@ int bdrv_reopen_multiple(AioContext *ctx, BlockReopenQueue *bs_queue, Error **er
>  
>      assert(bs_queue != NULL);
>  
> -    aio_context_release(ctx);
> -    bdrv_drain_all_begin();
> -    aio_context_acquire(ctx);
> -
>      QSIMPLEQ_FOREACH(bs_entry, bs_queue, entry) {
> +        assert(bs_entry->state.bs->quiesce_counter > 0);
>          if (bdrv_reopen_prepare(&bs_entry->state, bs_queue, &local_err)) {
>              error_propagate(errp, local_err);
>              goto cleanup;
> @@ -2955,8 +2960,6 @@ cleanup:
>      }
>      g_free(bs_queue);
>  
> -    bdrv_drain_all_end();
> -
>      return ret;
>  }
>  
> @@ -2966,12 +2969,18 @@ int bdrv_reopen(BlockDriverState *bs, int bdrv_flags, Error **errp)
>  {
>      int ret = -1;
>      Error *local_err = NULL;
> -    BlockReopenQueue *queue = bdrv_reopen_queue(NULL, bs, NULL, bdrv_flags);
> +    BlockReopenQueue *queue;
>  
> +    bdrv_subtree_drained_begin(bs);
> +
> +    queue = bdrv_reopen_queue(NULL, bs, NULL, bdrv_flags);
>      ret = bdrv_reopen_multiple(bdrv_get_aio_context(bs), queue, &local_err);
>      if (local_err != NULL) {
>          error_propagate(errp, local_err);
>      }
> +
> +    bdrv_subtree_drained_end(bs);
> +
>      return ret;
>  }
>  
> diff --git a/block/replication.c b/block/replication.c
> index e41e293d2b..b1ea3caa4b 100644
> --- a/block/replication.c
> +++ b/block/replication.c
> @@ -394,6 +394,9 @@ static void reopen_backing_file(BlockDriverState *bs, bool writable,
>          new_secondary_flags = s->orig_secondary_flags;
>      }
>  
> +    bdrv_subtree_drained_begin(s->hidden_disk->bs);
> +    bdrv_subtree_drained_begin(s->secondary_disk->bs);
> +
>      if (orig_hidden_flags != new_hidden_flags) {
>          reopen_queue = bdrv_reopen_queue(reopen_queue, s->hidden_disk->bs, NULL,
>                                           new_hidden_flags);
> @@ -409,6 +412,9 @@ static void reopen_backing_file(BlockDriverState *bs, bool writable,
>                               reopen_queue, &local_err);
>          error_propagate(errp, local_err);
>      }
> +
> +    bdrv_subtree_drained_end(s->hidden_disk->bs);
> +    bdrv_subtree_drained_end(s->secondary_disk->bs);
>  }
>  
>  static void backup_job_cleanup(BlockDriverState *bs)
> diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
> index de8e3de726..a6a70fc3dc 100644
> --- a/qemu-io-cmds.c
> +++ b/qemu-io-cmds.c
> @@ -2013,8 +2013,11 @@ static int reopen_f(BlockBackend *blk, int argc, char **argv)
>      opts = qopts ? qemu_opts_to_qdict(qopts, NULL) : NULL;
>      qemu_opts_reset(&reopen_opts);
>  
> +    bdrv_subtree_drained_begin(bs);
>      brq = bdrv_reopen_queue(NULL, bs, opts, flags);
>      bdrv_reopen_multiple(bdrv_get_aio_context(bs), brq, &local_err);
> +    bdrv_subtree_drained_end(bs);
> +
>      if (local_err) {
>          error_report_err(local_err);
>      } else {
> -- 
> 2.13.6
> 

Reviewed-by: Fam Zheng <famz@redhat.com>