On Thu, Jan 16, 2025 at 9:27 AM Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
> On 1/15/25 6:24 PM, Olga Kornievskaia wrote:
> > nfsd stores its network transports in a lwq (which is a lockless list)
> > llist has no ability to remove a particular entry which nfsd needs
> > to remove a listener thread.
>
> Note that scripts/get_maintainer.pl says that the maintainer of this
> file is:
>
> linux-kernel@xxxxxxxxxxxxxxx
>
> so that address should appear on the cc: list of this series. So
> should the list of reviewers for NFSD that appear in MAINTAINERS.
I will resend and include the mentioned list.
> ISTR Neil found the same gap in the llist API. I don't think it's
> possible to safely remove an item from the middle of an llist. Much
> of the complexity of the current svc thread scheduler is due to this
> complication.
>
> I think you will need to mark the listener as dead and find some
> way of safely dealing with it later.
A listener can only be removed if there are no active threads. This
code in nfsd_nl_listener_set_doit() won't allow it which happens
before we are manipulating the listener:
/* For now, no removing old sockets while server is running */
if (serv->sv_nrthreads && !list_empty(&permsocks)) {
list_splice_init(&permsocks, &serv->sv_permsocks);
spin_unlock_bh(&serv->sv_lock);
err = -EBUSY;
goto out_unlock_mtx;
}
>
>
> > Suggested-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > Signed-off-by: Olga Kornievskaia <okorniev@xxxxxxxxxx>
> > ---
> > include/linux/llist.h | 36 ++++++++++++++++++++++++++++++++++++
> > 1 file changed, 36 insertions(+)
> >
> > diff --git a/include/linux/llist.h b/include/linux/llist.h
> > index 2c982ff7475a..fe6be21897d9 100644
> > --- a/include/linux/llist.h
> > +++ b/include/linux/llist.h
> > @@ -253,6 +253,42 @@ static inline bool __llist_add(struct llist_node *new, struct llist_head *head)
> > return __llist_add_batch(new, new, head);
> > }
> >
> > +/**
> > + * llist_del_entry - remove a particular entry from a lock-less list
> > + * @head: head of the list to remove the entry from
> > + * @entry: entry to be removed from the list
> > + *
> > + * Walk the list, find the given entry and remove it from the list.
> > + * The caller must ensure that nothing can race in and change the
> > + * list while this is running.
> > + *
> > + * Returns true if the entry was found and removed.
> > + */
> > +static inline bool llist_del_entry(struct llist_head *head, struct llist_node *entry)
> > +{
> > + struct llist_node *pos;
> > +
> > + if (!head->first)
> > + return false;
> > +
> > + /* Is it the first entry? */
> > + if (head->first == entry) {
> > + head->first = entry->next;
> > + entry->next = entry;
> > + return true;
> > + }
> > +
> > + /* Find it in the list */
> > + llist_for_each(head->first, pos) {
> > + if (pos->next == entry) {
> > + pos->next = entry->next;
> > + entry->next = entry;
> > + return true;
> > + }
> > + }
> > + return false;
> > +}
> > +
> > /**
> > * llist_del_all - delete all entries from lock-less list
> > * @head: the head of lock-less list to delete all entries
>
>
> --
> Chuck Lever
>
