Re: [patch net-next v3 01/11] net: devlink: make sure that devlink_try_get() works with valid pointer during xarray iteration

[Jiri Pirko <jiri@resnulli.us>]

Thu, Jul 21, 2022 at 08:55:04PM CEST, jacob.e.keller@intel.com wrote:
>
>
>> -----Original Message-----
>> From: Jiri Pirko <jiri@resnulli.us>
>> Sent: Wednesday, July 20, 2022 10:45 PM
>> To: Keller, Jacob E <jacob.e.keller@intel.com>
>> Cc: netdev@vger.kernel.org; davem@davemloft.net; kuba@kernel.org;
>> idosch@nvidia.com; petrm@nvidia.com; pabeni@redhat.com;
>> edumazet@google.com; mlxsw@nvidia.com; saeedm@nvidia.com;
>> snelson@pensando.io
>> Subject: Re: [patch net-next v3 01/11] net: devlink: make sure that
>> devlink_try_get() works with valid pointer during xarray iteration
>> 
>> >Is it safe to rcu_read_unlock here while we're still in the middle of the array
>> processing? What happens if something else updates the xarray? is the
>> for_each_marked safe?
>> 
>> Sure, you don't need to hold rcu_read_lock during call to xa_for_each_marked.
>> The consistency of xarray is itself guaranteed. The only reason to take
>> rcu_read_lock outside is that the devlink pointer which is
>> rcu_dereference_check()'ed inside xa_for_each_marked() is still valid
>> once we devlink_try_get() it.
>> 
>
>Excellent, ok. Basically we need the RCU for protecting just the pointer until we get a reference to it separately.

Yep.


>
>Thanks!
>
>In that case:
>
>Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

Thanks. I will send v4 soon wrapping this up into helper as Jakub
requested.