On Tue, 18 Oct 2016 16:56:48 -0400
Steven Rostedt <rost...@goodmis.org> wrote:

> Is releasing the lock within a llist_for_each_entry_safe() actually safe? Is
> vmap_area_lock the one to protect the valist?
> That is llist_for_each_entry_safe(va, n_va, valist, purg_list) does:
>       for (va = llist_entry(valist, typeof(*va), purge_list);
>            &va->purge_list != NULL &&
>            n_va = llist_entry(va->purge_list.next, typeof(*n_va),
>                               purge_list, true);
>            pos = n)
> Thus n_va is pointing to the next element to process when we release the
> lock. Is it possible for another task to get into this same path and process
> the item that n_va is pointing to? Then when the preempted task comes back,
> grabs the vmap_area_lock, and then continues the loop with what n_va has,
> could that cause problems? That is, the next iteration after releasing the
> lock does va = n_va. What happens if n_va no longer exits?
> I don't know this code that well, and perhaps vmap_area_lock is not protecting
> the list and this is all fine.

Bah, nevermind. I missed the:

        valist = llist_del_all(&vmap_purge_list);

so yeah, all should be good.

Nothing to see here, move along please.

-- Steve

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