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?
-Toke
