Re: [Qemu-devel] [RFC PATCH] qcow2: Fix race in cache invalidation

[Kevin Wolf <kwolf@redhat.com>]

Am 25.09.2014 um 11:55 hat Alexey Kardashevskiy geschrieben:
> Right. Cool. So is below what was suggested? I am doublechecking as it does
> not solve the original issue - the bottomhalf is called first and then
> nbd_trip() crashes in qcow2_co_flush_to_os().
> 
> diff --git a/block.c b/block.c
> index d06dd51..1e6dfd1 100644
> --- a/block.c
> +++ b/block.c
> @@ -5037,20 +5037,22 @@ void bdrv_invalidate_cache(BlockDriverState *bs,
> Error **errp)
>      if (local_err) {
>          error_propagate(errp, local_err);
>          return;
>      }
> 
>      ret = refresh_total_sectors(bs, bs->total_sectors);
>      if (ret < 0) {
>          error_setg_errno(errp, -ret, "Could not refresh total sector count");
>          return;
>      }
> +
> +    bdrv_drain_all();
>  }

Try moving the bdrv_drain_all() call to the top of the function (at
least it must be called before bs->drv->bdrv_invalidate_cache).

> +static QEMUBH *migration_complete_bh;
> +static void process_incoming_migration_complete(void *opaque);
> +
>  static void process_incoming_migration_co(void *opaque)
>  {
>      QEMUFile *f = opaque;
> -    Error *local_err = NULL;
>      int ret;
> 
>      ret = qemu_loadvm_state(f);
>      qemu_fclose(f);

Paolo suggested to move eveything starting from here, but as far as I
can tell, leaving the next few lines here shouldn't hurt.

>      free_xbzrle_decoded_buf();
>      if (ret < 0) {
>          error_report("load of migration failed: %s", strerror(-ret));
>          exit(EXIT_FAILURE);
>      }
>      qemu_announce_self();
> 
>      bdrv_clear_incoming_migration_all();
> +
> +    migration_complete_bh = aio_bh_new(qemu_get_aio_context(),
> +                                       process_incoming_migration_complete,
> +                                       NULL);
> +    qemu_bh_schedule(migration_complete_bh);
> +}
> +
> +static void process_incoming_migration_complete(void *opaque)
> +{
> +    Error *local_err = NULL;
> +
>      /* Make sure all file formats flush their mutable metadata */
>      bdrv_invalidate_cache_all(&local_err);
>      if (local_err) {
>          qerror_report_err(local_err);
>          error_free(local_err);
>          exit(EXIT_FAILURE);
>      }
> 
>      if (autostart) {
>          vm_start();
>      } else {
>          runstate_set(RUN_STATE_PAUSED);
>      }
> +    qemu_bh_delete(migration_complete_bh);
> +    migration_complete_bh = NULL;
>  }

That part looks good to me. I hope moving bdrv_drain_all() does the
trick, otherwise there's somthing wrong with our reasoning.

Kevin