Re: 6.18.13 iwlwifi deadlock allocating cma while work-item is active.

[Johannes Berg <johannes@sipsolutions.net>]

On Tue, 2026-03-03 at 10:52 -1000, Tejun Heo wrote:
> Hello,
> 
> On Tue, Mar 03, 2026 at 12:49:24PM +0100, Johannes Berg wrote:
> > Fair. I don't know, I don't think there's anything that even shows that
> > there's a dependency between the two workqueues and the
> > "((wq_completion)events_unbound)" and "((wq_completion)events)", and
> > there would have to be for it to deadlock this way because of that?
> > 
> > But one is mm_percpu_wq and the other is system_percpu_wq.
> > 
> > Tejun, does the workqueue code somehow introduce a dependency between
> > different per-CPU workqueues that's not modelled in lockdep?
> 
> Hopefully not. Kinda late to the party. Why isn't mm_percpu_wq making
> forward progress? That should in all circumstances. What's the work item and
> kworker doing?

Oh and in addition: the worker that's kicked off by
__lru_add_drain_all() doesn't really seem to do anything long-running?
It's lru_add_drain_per_cpu(), which is lru_add_and_bh_lrus_drain(),
which would appear to be entirely non-sleepable code (holding either
local locks or having irqs disabled.) It also doesn't show up in the
log, apparently, hence my question about strange dependencies.

johannes