Am 23.05.2023 um 23:39 hat Fabiano Rosas geschrieben:
> We're about to move calls to 'fstat' into the thread-pool to avoid
> blocking VCPU threads should the system call take too long.
>
> To achieve that we first need to make sure none of its callers is
> holding the aio_context lock, otherwise yielding before scheduling the
> aiocb handler would result in a deadlock when the qemu_global_mutex is
> released and another thread tries to acquire the aio_context.
>
> Signed-off-by: Fabiano Rosas <faro...@suse.de>
> ---
> block/qapi.c | 22 +++++++++++++++++++++-
> 1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/block/qapi.c b/block/qapi.c
> index ae6cd1c2ff..cd197abf1f 100644
> --- a/block/qapi.c
> +++ b/block/qapi.c
> @@ -222,6 +222,26 @@ int bdrv_query_snapshot_info_list(BlockDriverState *bs,
> return 0;
> }
>
> +static int64_t bdrv_get_actual_size(BlockDriverState *bs)
> +{
> + int64_t size;
> + AioContext *old_ctx = NULL;
> +
> + if (qemu_in_coroutine()) {
Hm. Why can't we make sure that it always runs in a coroutine?
Callers:
* bdrv_query_block_node_info(). This functions seems to be completely
unused, we can remove it.
* bdrv_query_image_info(). Called by bdrv_block_device_info() and itself.
bdrv_block_device_info() could become a co_wrapper after swapping the
first two parameters so that it runs in the AioContext of @bs.
* bdrv_query_block_graph_info(). Only called by qemu-img. Could become a
co_wrapper_bdrv_rdlock.
> + aio_context_release(bdrv_get_aio_context(bs));
> + old_ctx = bdrv_co_enter(bs);
I think this is the wrong function to do this. The caller should already
make sure that it's in the right AioContext.
> + }
> +
> + size = bdrv_get_allocated_file_size(bs);
> +
> + if (qemu_in_coroutine() && old_ctx) {
> + bdrv_co_leave(bs, old_ctx);
> + aio_context_acquire(bdrv_get_aio_context(bs));
> + }
> +
> + return size;
> +}
Kevin
