Re: [PATCH for-8.0] ide: Fix manual in-flight count for TRIM BH

[Paolo Bonzini]

On 3/9/23 12:44, Hanna Czenczek wrote:
> +     *
> +     * Note that TRIM operations call blk_aio_pdiscard() multiple
> +     * times (and finally increment s->blk's in-flight counter while
> +     * ide_trim_bh_cb() is scheduled), so we have to loop blk_drain()
> +     * until the whole operation is done.
>        */
>       if (s->bus->dma->aiocb) {
>           trace_ide_cancel_dma_sync_remaining();
> -        blk_drain(s->blk);
> -        assert(s->bus->dma->aiocb == NULL);
> +        while (s->bus->dma->aiocb) {
> +            blk_drain(s->blk);
> +        }

I think having to do this is problematic, because the blk_drain should 
leave no pending operation.

Here it seems okay because you do it in a controlled situation, but the 
main thread can also issue blk_drain(), or worse bdrv_drained_begin(), 
and there would be pending I/O operations when it returns.

Unfortunately I don't have a solution (I'm not considering the idea of 
using disable_request_queuing and having even more atomics magic in 
block/block-backend.c), but I'll read the thread.

Paolo