Re: [RFC] deadlock with flush_work() in UAS

From: Tejun Heo
Date: Thu Jun 20 2019 - 10:15:20 EST


On Tue, Jun 18, 2019 at 11:59:39AM -0400, Alan Stern wrote:
> > > Even if you disagree, perhaps we should have a global workqueue with a
> > > permanently set noio flag. It could be shared among multiple drivers
> > > such as uas and the hub driver for purposes like this. (In fact, the
> > > hub driver already has its own dedicated workqueue.)
> >
> > That is a good idea. But does UAS need WQ_MEM_RECLAIM?
> These are good questions, and I don't have the answers. Perhaps Tejun
> or someone else on LKML can help.

Any device which may host a filesystem or swap needs to use
WQ_MEM_RECLAIM workqueues on anything which may be used during normal
IOs including e.g. error handling which may be invoked. One
WQ_MEM_RECLAIM workqueue guarantees one level of concurrency for all
its tasks regardless of memory situation, so as long as there's no
interdependence between work items, the workqueue can be shared.