On Wed, 31 Jan 2024, Tejun Heo wrote:
> Hello,
>
> On Wed, Jan 31, 2024 at 10:19:07PM +0100, Mikulas Patocka wrote:
> > > @@ -83,7 +83,7 @@ struct dm_verity_io {
> > > struct bvec_iter iter;
> > >
> > > struct work_struct work;
> > > - struct tasklet_struct tasklet;
> > > + struct work_struct bh_work;
> > >
> > > /*
> > > * Three variably-size fields follow this struct:
> >
> > Do we really need two separate work_structs here? They are never submitted
> > concurrently, so I think that one would be enough. Or, am I missing
> > something?
>
> 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.
> However, the followings might be useful to keep on mind:
>
> - work_struct is pretty small - 4 pointers.
>
> - INIT_WORK() on a queued work item isn't gonna be pretty.
>
> - Flushing and no-concurrent-execution guarantee are broken on INIT_WORK().
> e.g. If you queue_work(), INIT_WORK(), flush_work(), the flush isn't
> actually going to wait for the work item to finish. Also, if you do
> queue_work(), INIT_WORK(), queue_work(), the two queued work item
> instances may end up running concurrently.
>
> Muxing a single work item carries more risks of subtle bugs, but in some
> cases, the way it's used is clear (e.g. sequential chaining) and that's
> fine.
The code doesn't call INIT_WORK() on a queued work item and it doesn't
flush the workqueue (it destroys it only in a situation when there are no
work items running) so I think it's safe to use just one work_struct.
Mikulas
