On 17/07/2018 10:27 PM, Daniel Borkmann wrote:
On 07/17/2018 06:47 PM, Alexei Starovoitov wrote:
On Tue, Jul 17, 2018 at 06:10:38PM +0300, Tariq Toukan wrote:
Fix the warning below by calling rhashtable_lookup under
RCU read lock.
...
mutex_lock(&mem_id_lock);
+ rcu_read_lock();
xa = rhashtable_lookup(mem_id_ht, &id, mem_id_rht_params);
+ rcu_read_unlock();
if (!xa) {
if it's an actual bug rcu_read_unlock seems to be misplaced.
It silences the warn, but rcu section looks wrong.
I think that whole piece in __xdp_rxq_info_unreg_mem_model() should be:
mutex_lock(&mem_id_lock);
xa = rhashtable_lookup_fast(mem_id_ht, &id, mem_id_rht_params);
if (xa && rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params) ==
0)
call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
mutex_unlock(&mem_id_lock);
Technically the RCU read side plus rhashtable_lookup() is the same, but lets
use proper api. From the doc (https://lwn.net/Articles/751374/) object removal
is wrapped around the RCU read side additionally, but in our case we're behind
mem_id_lock for insertion/removal serialization.
Cheers,
Daniel
Just as Daniel stated, I think there's no actual bug here, but we still
want to silence the RCU warning.
Alexei, did you mean getting the if statement into the RCU lock critical
section?
