Re: [PATCH net] nfp: fix rcu_read_lock/unlock while rcu_derefrencing

On Tue, May 09, 2023 at 07:40:13PM -0700, Jakub Kicinski wrote:

On Tue, 9 May 2023 08:06:32 +0200 Louis Peens wrote:

...

+static inline +struct net_device *nfp_app_dev_get_locked(struct nfp_app *app, u32 id,

_locked() in what way? RCU functions typically use an _rcu suffix, no?

We were discussing the naming during internal review, for some reason didn't think about using _rcu, will update if there is a v2.

...

• 			  bool *redir_egress)
  

+{

• struct net_device *dev;
• if (unlikely(!app || !app->type->dev_get))

• return NULL;
  

• rcu_read_lock();
• dev = app->type->dev_get(app, id, redir_egress);
• rcu_read_unlock();
• return dev;

this looks very suspicious, RCU takes care primarily of the lifetime of objects, in this case dev. Returning it after dropping the lock seems wrong.

If the context is safe maybe it's a better idea to change the condition in rcu_dereference_check() to include rcu_read_lock_bh_held()?

Thanks, will take a closer look at this.

-- pw-bot: cr