Re: [PATCH v2 2/2] btrfs: fix compressed write bio attribution

[David Sterba <dsterba@suse.cz>]

On Thu, Dec 12, 2019 at 10:19:34AM -0800, Dennis Zhou wrote:
> From a0569aebde08e31e994c92d0b70befb84f7f5563 Mon Sep 17 00:00:00 2001
> From: Dennis Zhou <dennis@kernel.org>
> Date: Wed, 11 Dec 2019 15:20:15 -0800
> 
> Bio attribution is handled at bio_set_dev() as once we have a device, we
> have a corresponding request_queue and then can derive the current css.
> In special cases, we want to attribute to bio to someone else. This can
> be done by calling bio_associate_blkg_from_css() or
> kthread_associate_blkcg() depending on the scenario. Btrfs does this for
> compressed writeback as they are handled by kworkers, so the latter can
> be done here.
> 
> Commit 1a41802701ec ("btrfs: drop bio_set_dev where not needed") removes
> early bio_set_dev() calls prior to submit_stripe_bio(). This breaks the
> above assumption that we'll have a request_queue when we are doing
> association. To fix this, switch to using kthread_associate_blkcg().

Can be kthread_associate_blkcg used also for submit_extent_page that
calls bio_associate_blkg_from_css indirectly when initializing wbc?

2996                 bio_set_dev(bio, bdev);
2997                 wbc_init_bio(wbc, bio);
2998                 wbc_account_cgroup_owner(wbc, page, page_size);

wbc_init_bio:

	if (wbc)
		bio_associate_blkg_from_css();