linux-kernel - Re: [PATCH 8/8] dm-verity: Convert from tasklet to BH workqueue

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Date: Tue, 20 Feb 2024 14:44:29 -0500
From: Mike Snitzer <snitzer@...nel.org>
To: Tejun Heo <tj@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Mikulas Patocka <mpatocka@...hat.com>, linux-kernel@...r.kernel.org,
	dm-devel@...ts.linux.dev, msnitzer@...hat.com, ignat@...udflare.com,
	damien.lemoal@....com, bob.liu@...cle.com, houtao1@...wei.com,
	peterz@...radead.org, mingo@...nel.org, netdev@...r.kernel.org,
	allen.lkml@...il.com, kernel-team@...a.com,
	Alasdair Kergon <agk@...hat.com>
Subject: Re: [PATCH 8/8] dm-verity: Convert from tasklet to BH workqueue

On Wed, Jan 31 2024 at  7:19P -0500,
Mike Snitzer <snitzer@...nel.org> wrote:

> On Wed, Jan 31 2024 at  7:04P -0500,
> Tejun Heo <tj@...nel.org> wrote:
> 
> > Hello, Linus.
> > 
> > On Wed, Jan 31, 2024 at 03:19:01PM -0800, Linus Torvalds wrote:
> > > On Wed, 31 Jan 2024 at 13:32, Tejun Heo <tj@...nel.org> wrote:
> > > >
> > > > I don't know, so just did the dumb thing. If the caller always guarantees
> > > > that the work items are never queued at the same time, reusing is fine.
> > > 
> > > So the reason I thought it would be a good cleanup to introduce that
> > > "atomic" workqueue thing (now "bh") was that this case literally has a
> > > switch between "use tasklets' or "use workqueues".
> > > 
> > > So it's not even about "reusing" the workqueue, it's literally a
> > > matter of making it always just use workqueues, and the switch then
> > > becomes just *which* workqueue to use - system or bh.
> > 
> > Yeah, that's how the dm-crypt got converted. The patch just before this one.
> > This one probably can be converted the same way. I don't see the work item
> > being re-initialized. It probably is better to initialize the work item
> > together with the enclosing struct and then just queue it when needed.
> 
> Sounds good.
>  
> > Mikulas, I couldn't decide what to do with the "try_verify_in_tasklet"
> > option and just decided to do the minimal thing hoping that someone more
> > familiar with the code can take over the actual conversion. How much of user
> > interface commitment is that? Should it be renamed or would it be better to
> > leave it be?
> 
> cryptsetup did add support for it, so I think it worthwhile to
> preserve the option; but it'd be fine to have it just be a backward
> compatible alias for a more appropriately named option?

Hey Tejun,

I'm not sure where things stand with the 6.9 workqueue changes to add
BH workqueue.  I had a look at your various branches and I'm not
seeing where you might have staged any conversion patches (like this
dm-verity one).

I just staged various unrelated dm-verity and dm-crypt 6.8 fixes from
Mikulas that I'll be sending to Linus later this week (for v6.8-rc6).
Those changes required rebasing 'dm-6.9' because of conflicts, here is
the dm-6.9 branch:
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-6.9

So we'll definitely need to rebase your changes on dm-6.9 to convert
dm-crypt and dm-verity over to your BH workqueue.  Are you OK with
doing that or would you prefer I merge some 6.9 workqueue branch that
you have into dm-6.9? And then Mikulas and I work to make the required
DM target conversion changes?

However you'd like to do it: please let me know where you have the
latest 6.9 code the adds BH workqueue (and if you have DM target
conversion code that reflects your latest).

Thanks,
Mike