Re: [PATCH 4/8] FOLD: block: change the defer in task context interface to be procedural

[Matthew Wilcox <willy@infradead.org>]

On Thu, Apr 09, 2026 at 06:02:17PM +0200, Christoph Hellwig wrote:
> @@ -1836,9 +1837,7 @@ void bio_endio(struct bio *bio)
>  	}
>  #endif
>  
> -	if (!in_task() && bio_flagged(bio, BIO_COMPLETE_IN_TASK))
> -		bio_queue_completion(bio);
> -	else if (bio->bi_end_io)
> +	if (bio->bi_end_io)
>  		bio->bi_end_io(bio);

What I liked about this before is that we had one central place that
needed to be changed.  This change means that every bi_end_io now needs
to check whether the BIO can be completed in its context.

> +++ b/fs/buffer.c
> @@ -2673,6 +2673,9 @@ static void end_bio_bh_io_sync(struct bio *bio)
>  {
>  	struct buffer_head *bh = bio->bi_private;
>  
> +	if (buffer_dropbehind(bh) && bio_complete_in_task(bio))
> +		return;

I really don't like this.  It assumes there's only one reason to
complete in task context -- whether the buffer belongs to a dropbehind
folio.  I want there to be other reasons.  Why would you introduce the
new BH_dropbehind flag instead of checking BIO_COMPLETE_IN_TASK?

>  	struct iomap_ioend *ioend = iomap_ioend_from_bio(bio);
>  
> +	/* Page cache invalidation cannot be done in irq context. */
> +	if (ioend->io_flags & IOMAP_IOEND_DONTCACHE) {
> +		if (bio_complete_in_task(bio))
> +			return;
> +	}

I thought we agreed to kill off IOMAP_IOEND_DONTCACHE?