[PATCH V2] UBI: add ubi_lnum_purge function to clear work queue for a lnum

[Joel Reardon]

> Take the work_sem at the beginning. Release at the very end.
>
> Then you can do something like this:
>
> int found = 1;
>
> while (found) {
> 	found = 0;
>
> 	spin_lock(&ubi->wl_lock);
> 	list_for_each_entry(wrk, tmp, &ubi->works, list) {
> 		if (wrk->lnum == lnum) {
> 			list_del(&wrk->list);
> 			ubi->works_count -= 1;
> 			ubi_assert(ubi->works_count >= 0);
> 			spin_unlock(&ubi->wl_lock);
>
> 			err = wrk->func(ubi, wrk, 0);
> 			if (err)
> 				return err;
>
> 			spin_lock(&ubi->wl_lock);
> 			found = 1;
> 			break;
> 	}
> 	spin_unlock(&ubi->wl_lock);
> }
>


If I use list_for_each_entry_safe(), it protects against deleting as it
iterates. If I take the work_sem first, is it okay to do a simple
traversal instead of one traversal per removed item? Even if another
thread adds new work for the same vol_id/lnum, its okay, because the
caller of this function only cares about vol_id/lnums erasures that
it knows are currently on the worklist.

Cheers,
Joel Reardon