linux-kernel - Re: [RFC PATCH 1/3] workqueue: Add an interface to taint workqueue lockdep with reclaim

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Message-ID: <aQIthmQmKfztyaQZ@slm.duckdns.org>
Date: Wed, 29 Oct 2025 05:06:46 -1000
From: Tejun Heo <tj@...nel.org>
To: Matthew Brost <matthew.brost@...el.com>
Cc: Christian König <christian.koenig@....com>,
	intel-xe@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, jiangshanlai@...il.com,
	simona.vetter@...ll.ch, pstanner@...hat.com, dakr@...nel.org
Subject: Re: [RFC PATCH 1/3] workqueue: Add an interface to taint workqueue
 lockdep with reclaim

Hello,

On Tue, Oct 28, 2025 at 01:16:43PM -0700, Matthew Brost wrote:
> On Tue, Oct 28, 2025 at 10:32:54AM +0100, Christian König wrote:
> > On 10/21/25 23:39, Matthew Brost wrote:
> > > Drivers often use workqueues that are in the reclaim path (e.g., DRM
> > > scheduler workqueues). It is useful to teach lockdep that memory cannot
> > > be allocated on these workqueues. Add an interface to taint workqueue
> > > lockdep with reclaim.
> > 
> > Oh that is so wonderfully evil. I'm absolutely in favor of doing this.
> > 
> > But can't we check for the existing WQ_MEM_RECLAIM flag in the workqueue handling instead?
> > 
> 
> Tejun suggested tying the lockdep annotation to WQ_MEM_RECLAIM, but the
> entire kernel explodes because many workqueues throughout Linux don’t
> adhere to this rule. Here's a link to my latest reply to Tejun [1].

How about making it a WQ flag?

Thanks.

-- 
tejun