[RFC PATCH v1 05/17] block: add bio_alloc_atomic() for atomic bio users

[Christoph Hellwig]

On Sun, Jul 05, 2026 at 03:51:12AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai at fygo.io>
> 
> Add bio_alloc_atomic() for callers that need a GFP_ATOMIC bio from the
> default bio set but cannot safely pass a bdev during allocation. The
> helper returns an unattached bio, leaving callers to set bi_bdev and
> attach blkcg state explicitly before submission.
> 
> Use the helper for virtio-pmem flush child bios and OCFS2 heartbeat I/O.
> Both allocate bios from atomic paths and must avoid creating missing blkgs
> once blkg creation is protected by q->blkcg_mutex. virtio-pmem clones the
> parent bio's blkg association; OCFS2 binds heartbeat I/O to the root blkg.

Let's kill off the concept of atomic bio allocations instead.
Joseph already has an outstanding patch for nd_virtio that needs a little
bit more work, and ocfs2 should be easy enough as well.