Re: [PATCH] cfg80211: Pass lockdep expression to RCU lists

From: Arend Van Spriel
Date: Wed Feb 19 2020 - 16:33:34 EST

On 2/19/2020 10:29 PM, Johannes Berg wrote:
On Wed, 2020-02-19 at 22:27 +0100, Arend Van Spriel wrote:
On 2/19/2020 10:13 AM, Johannes Berg wrote:
On Wed, 2020-02-19 at 14:41 +0530, Amol Grover wrote:
- WARN_ON_ONCE(!rcu_read_lock_held() && !lockdep_rtnl_is_held());
- list_for_each_entry_rcu(pos, &rdev->sched_scan_req_list, list) {
+ list_for_each_entry_rcu(pos, &rdev->sched_scan_req_list, list,
+ lockdep_rtnl_is_held()) {

Huh, I didn't even know you _could_ do that :)

Me neither ;-). Above you are removing the WARN_ON_ONCE() entirely.
Would it not be good to keep the WARN_ON_ONCE() with only the
!rcu_read_lock_held() check.

Not needed, the macro expansion will already contain
rcu_read_lock_any_held() just like in all the other cases where you pass
a lockdep condition to RCU helpers.

Ah, yes. I see it in __list_check_rcu().