Peter, I am all confused and I am still trying to understand your email.
In particular, because I no longer understand the lockdep annotations in
workqueue.c, it turns out I forgot everything...
On 08/22, Peter Zijlstra wrote:
>
> I am however slightly puzzled by the need of flush_work() to take Q,
> what deadlock potential is there?
Do you really mean flush_work()? Or start_flush_work() ?
> It was added by Oleg in commit:
>
> a67da70dc095 ("workqueues: lockdep annotations for flush_work()")
No, these annotations were moved later into start_flush, iiuc...
This
lock_map_acquire(&work->lockdep_map);
lock_map_release(&work->lockdep_map);
was added by another commit 0976dfc1d0cd80a4e9dfaf87bd8744612bde475a
"workqueue: Catch more locking problems with flush_work()", and at
first glance it is fine.
At the same time, I have a vague feeling that (perhaps) we can remove
these 2 annotations if we change process_one_work() and start_flush_work(),
not sure...
Oleg.
