On Fri, Oct 18, 2019 at 12:26:55PM +0200, Toke Høiland-Jørgensen wrote:
> Martin Lau <kafai@xxxxxx> writes:
>
> > On Thu, Oct 17, 2019 at 12:52:32PM +0200, Toke Høiland-Jørgensen wrote:
> >> It seems I forgot to add handling of devmap_hash type maps to the device
> >> unregister hook for devmaps. This omission causes devices to not be
> >> properly released, which causes hangs.
> >>
> >> Fix this by adding the missing handler.
> >>
> >> Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by hashed index")
> >> Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> >> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> >> ---
> >> v2:
> >> - Grab the update lock while walking the map and removing entries.
> >>
> >> kernel/bpf/devmap.c | 37 +++++++++++++++++++++++++++++++++++++
> >> 1 file changed, 37 insertions(+)
> >>
> >> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> >> index d27f3b60ff6d..a0a1153da5ae 100644
> >> --- a/kernel/bpf/devmap.c
> >> +++ b/kernel/bpf/devmap.c
> >> @@ -719,6 +719,38 @@ const struct bpf_map_ops dev_map_hash_ops = {
> >> .map_check_btf = map_check_no_btf,
> >> };
> >>
> >> +static void dev_map_hash_remove_netdev(struct bpf_dtab *dtab,
> >> + struct net_device *netdev)
> >> +{
> >> + unsigned long flags;
> >> + int i;
> > dtab->n_buckets is u32.
>
> Oh, right, will fix.
>
> >> +
> >> + spin_lock_irqsave(&dtab->index_lock, flags);
> >> + for (i = 0; i < dtab->n_buckets; i++) {
> >> + struct bpf_dtab_netdev *dev, *odev;
> >> + struct hlist_head *head;
> >> +
> >> + head = dev_map_index_hash(dtab, i);
> >> + dev = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),
> > The spinlock has already been held. Is rcu_deref still needed?
>
> I guess it's not strictly needed, but since it's an rcu-protected list,
> and hlist_first_rcu() returns an __rcu-annotated type, I think we will
> get a 'sparse' warning if it's omitted, no?
>
> And since it's just a READ_ONCE, it doesn't actually hurt since this is
> not the fast path, so I'd lean towards just keeping it? WDYT?
>
Can hlist_for_each_safe() be used instead then?
A bonus is the following long line will go away.
I think the change will be simpler also.
> + struct bpf_dtab_netdev,
> + index_hlist);
> +
> + while (dev) {
> + odev = (netdev == dev->dev) ? dev : NULL;
> + dev = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&dev->index_hlist)),
> + struct bpf_dtab_netdev,
> + index_hlist);
> +
> + if (odev) {
> + hlist_del_rcu(&odev->index_hlist);
> + call_rcu(&odev->rcu,
> + __dev_map_entry_free);
> + }
> + }
> + }
> + spin_unlock_irqrestore(&dtab->index_lock, flags);
> +}
> +
