Re: [RFC PATCH 0/2] workqueue: Add wornings and check WQ flags usage

[Marco Crivellari]

On Fri, May 15, 2026 at 2:17 PM Breno Leitao <leitao@xxxxxxxxxx> wrote:
>
> On Thu, May 14, 2026 at 11:23:52AM +0200, Marco Crivellari wrote:
> > Hi,
> >
> > Currently system_wq and system_unbound_wq can still be used and no message
> > is printed. To avoid further use of them, add a warning and route the
> > workqueue on system_percpu_wq or system_dfl_wq.
> >
> > Similar scenario for WQ_PERCPU and WQ_UNBOUND. Currently there are still
> > users that use alloc_workqueue(,0,). To avoid such situations, a couple
> > of checks have been added:
> >
> >   - if neither of the flag is present, set WQ_PERCPU
> >   - if both are present, remove WQ_PERCPU
> >
> > Along with these, a warning will be printed.
>
> How many users will seee this warning once this patch lands?

About WQ_*, I would say (currently, v7.1-rc3) there are 8 users, but 4
of them are accepted (2 by Tejun, because we didn't receive replies
for a long time) and the other 2 will likely be accepted in May (they
are new and were sent a few days ago).

About the deprecated workqueues:

system_wq: 8 (-3, accepted, 1 handled by Tejun)
system_unbound_wq: 19

Among the 19, 2 are new (recently introduced and still pending
changes), and Tejun handles other two of them. Note that 7 of the
remaining 15 are part of the same series.

I think the most important change, because it is also a blocker, is
requiring alloc_workqueue() users to have one of the flags. This will
allow us to switch to the unbound workqueue as default, removing
`WQ_UNBOUND` as well. We cannot of course do that now.

What do you think?

Thanks!

-- 

Marco Crivellari

SUSE Labs