Re: [Qemu-devel] [PATCH] fixup! block-migration: acquire AioContext as necessary

[Fam Zheng <famz@redhat.com>]

On Fri, 02/19 16:10, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  migration/block.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/migration/block.c b/migration/block.c
> index 3bfa908..eea4788 100644
> --- a/migration/block.c
> +++ b/migration/block.c
> @@ -54,6 +54,7 @@ typedef struct BlkMigDevState {
>      int shared_base;
>      int64_t total_sectors;
>      QSIMPLEQ_ENTRY(BlkMigDevState) entry;
> +    Error *blocker;
>  
>      /* Only used by migration thread.  Does not need a lock.  */
>      int bulk_completed;
> @@ -68,9 +69,10 @@ typedef struct BlkMigDevState {
>      /* Protected by block migration lock.  */
>      int64_t completed_sectors;
>  
> -    /* Protected by iothread lock / AioContext.  */
> +    /* During migration this is protected by iothread lock / AioContext.
> +     * Allocation and free happen during setup and cleanup respectively.
> +     */
>      BdrvDirtyBitmap *dirty_bitmap;
> -    Error *blocker;
>  } BlkMigDevState;
>  
>  typedef struct BlkMigBlock {
> @@ -339,9 +341,10 @@ static int set_dirty_tracking(void)
>      int ret;
>  
>      QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
> -        /* Creating/dropping dirty bitmaps only requires the big QEMU lock.  */
> +        aio_context_acquire(bdrv_get_aio_context(bmds->bs));
>          bmds->dirty_bitmap = bdrv_create_dirty_bitmap(bmds->bs, BLOCK_SIZE,
>                                                        NULL, NULL);
> +        aio_context_release(bdrv_get_aio_context(bmds->bs));
>          if (!bmds->dirty_bitmap) {
>              ret = -errno;
>              goto fail;
> @@ -352,7 +355,9 @@ static int set_dirty_tracking(void)
>  fail:
>      QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
>          if (bmds->dirty_bitmap) {
> +            aio_context_acquire(bdrv_get_aio_context(bmds->bs));
>              bdrv_release_dirty_bitmap(bmds->bs, bmds->dirty_bitmap);
> +            aio_context_release(bdrv_get_aio_context(bmds->bs));
>          }
>      }
>      return ret;
> @@ -365,8 +370,9 @@ static void unset_dirty_tracking(void)
>      BlkMigDevState *bmds;
>  
>      QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
> -        /* Creating/dropping dirty bitmaps only requires the big QEMU lock.  */
> +        aio_context_acquire(bdrv_get_aio_context(bmds->bs));
>          bdrv_release_dirty_bitmap(bmds->bs, bmds->dirty_bitmap);
> +        aio_context_release(bdrv_get_aio_context(bmds->bs));
>      }
>  }
>  
> -- 
> 2.5.0
> 

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

BTW, could you also explain the blk_mig_lock() question (*) I had?

*: https://lists.gnu.org/archive/html/qemu-devel/2016-02/msg03317.html

Fam